gradle: Fix Gradle 6 warnings

Most of these are easy "replace X with Y."

The CreateStartScripts changes were because the scripts were being included in
the output zip/tar multiple times. The was because they were all using the same
output directory, and the entire output directory was being included for each.
The output directory tmp/ was particularly poor because other tasks were
dumping things into it, so our zip/tar was including those junk files as well.
diff --git a/benchmarks/build.gradle b/benchmarks/build.gradle
index b3137ca..b653a9d 100644
--- a/benchmarks/build.gradle
+++ b/benchmarks/build.gradle
@@ -60,7 +60,7 @@
     defaultJvmOpts = [
         "-javaagent:" + configurations.alpnagent.asPath
     ].plus(vmArgs)
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
@@ -70,14 +70,14 @@
     defaultJvmOpts = [
         "-javaagent:" + configurations.alpnagent.asPath
     ].plus(vmArgs)
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
 task qps_server(type: CreateStartScripts) {
     mainClassName = "io.grpc.benchmarks.qps.AsyncServer"
     applicationName = "qps_server"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
@@ -87,7 +87,7 @@
     defaultJvmOpts = [
         "-javaagent:" + configurations.alpnagent.asPath
     ].plus(vmArgs)
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
diff --git a/build.gradle b/build.gradle
index 083475b..aaf4794 100644
--- a/build.gradle
+++ b/build.gradle
@@ -10,7 +10,6 @@
 
 subprojects {
     apply plugin: "checkstyle"
-    apply plugin: "maven"
     apply plugin: "idea"
     apply plugin: "signing"
     apply plugin: "jacoco"
@@ -286,7 +285,7 @@
     jacoco { toolVersion = "0.8.2" }
 
     checkstyle {
-        configDir = file("$rootDir/buildscripts")
+        configDirectory = file("$rootDir/buildscripts")
         toolVersion = "6.17"
         ignoreFailures = false
         if (rootProject.hasProperty("checkstyle.ignoreFailures")) {
@@ -315,7 +314,7 @@
         targetCompatibility = 1.7
 
         dependencies {
-            testCompile libraries.junit,
+            testImplementation libraries.junit,
                     libraries.mockito,
                     libraries.truth
         }
diff --git a/gae-interop-testing/gae-jdk8/build.gradle b/gae-interop-testing/gae-jdk8/build.gradle
index 5991b20..8ed1bc5 100644
--- a/gae-interop-testing/gae-jdk8/build.gradle
+++ b/gae-interop-testing/gae-jdk8/build.gradle
@@ -20,7 +20,7 @@
             url "https://maven-central.storage-download.googleapis.com/maven2/" }
     }
     dependencies {
-        classpath 'com.google.cloud.tools:appengine-gradle-plugin:1.3.5'
+        classpath 'com.google.cloud.tools:appengine-gradle-plugin:2.3.0'
         classpath 'com.squareup.okhttp:okhttp:2.7.4'
     }
 }
@@ -75,6 +75,7 @@
 
     deploy {
         // deploy configuration
+        projectId = 'GCLOUD_CONFIG'
         // default - stop the current version
         stopPreviousVersion = System.getProperty('gaeStopPreviousVersion') ?: true
         // default - do not make this the promoted version
diff --git a/interop-testing/build.gradle b/interop-testing/build.gradle
index 5f529c6..c4ddcc5 100644
--- a/interop-testing/build.gradle
+++ b/interop-testing/build.gradle
@@ -63,7 +63,7 @@
     defaultJvmOpts = [
         "-javaagent:JAVAAGENT_APP_HOME" + configurations.alpnagent.singleFile.name
     ]
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
     doLast {
         unixScript.text = unixScript.text.replace('JAVAAGENT_APP_HOME', '\$APP_HOME/lib/')
@@ -74,21 +74,21 @@
 task test_server(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.TestServiceServer"
     applicationName = "test-server"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
 task reconnect_test_client(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.ReconnectTestClient"
     applicationName = "reconnect-test-client"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
 task stresstest_client(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.StressTestClient"
     applicationName = "stresstest-client"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
     defaultJvmOpts = [
         "-verbose:gc",
@@ -99,14 +99,14 @@
 task http2_client(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.Http2Client"
     applicationName = "http2-client"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
 task grpclb_long_lived_affinity_test_client(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.GrpclbLongLivedAffinityTestClient"
     applicationName = "grpclb-long-lived-affinity-test-client"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
     defaultJvmOpts = [
         "-Dio.grpc.internal.DnsNameResolverProvider.enable_service_config=true"
@@ -116,8 +116,8 @@
 task grpclb_fallback_test_client (type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.GrpclbFallbackTestClient"
     applicationName = "grpclb-fallback-test-client"
-    outputDir = new File(project.buildDir, 'tmp')
-    classpath = jar.outputs.files + configurations.runtime
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
+    classpath = startScripts.classpath
     defaultJvmOpts = [
         "-Dio.grpc.internal.DnsNameResolverProvider.enable_service_config=true"
     ]
@@ -126,14 +126,14 @@
 task xds_test_client(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.XdsTestClient"
     applicationName = "xds-test-client"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
 task xds_test_server(type: CreateStartScripts) {
     mainClassName = "io.grpc.testing.integration.XdsTestServer"
     applicationName = "xds-test-server"
-    outputDir = new File(project.buildDir, 'tmp')
+    outputDir = new File(project.buildDir, 'tmp/scripts/' + name)
     classpath = startScripts.classpath
 }
 
diff --git a/settings.gradle b/settings.gradle
index 2891d91..9592c7e 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -9,7 +9,7 @@
         id "digital.wup.android-maven-publish" version "3.6.2"
         id "me.champeau.gradle.japicmp" version "0.2.5"
         id "me.champeau.gradle.jmh" version "0.5.0"
-        id "net.ltgt.errorprone" version "0.8.1"
+        id "net.ltgt.errorprone" version "1.2.1"
         id "ru.vyarus.animalsniffer" version "1.5.0"
     }
     resolutionStrategy {
diff --git a/testing-proto/build.gradle b/testing-proto/build.gradle
index 145ded4..f12fe92 100644
--- a/testing-proto/build.gradle
+++ b/testing-proto/build.gradle
@@ -12,7 +12,7 @@
             project(':grpc-stub')
     compileOnly libraries.javax_annotation
     testImplementation libraries.truth
-    testRuntime libraries.javax_annotation
+    testRuntimeOnly libraries.javax_annotation
 }
 
 configureProtoCompilation()