Fix playground builds

Playground does not set OUT_DIR, so we need to use checkoutRoot for
placing koltin project persistent dir.

Test: ./gradlew tasks in playground-projects/core-playground/
Change-Id: Ibac60b1b9e515d51e0269b7effdb812fcf6d9237
diff --git a/buildSrc/settings.gradle b/buildSrc/settings.gradle
index 65a9e34..a73e8cf 100644
--- a/buildSrc/settings.gradle
+++ b/buildSrc/settings.gradle
@@ -16,11 +16,10 @@
 
 apply from: "settingsScripts/out-setup.groovy"
 getGradle().beforeProject { project ->
-    init.chooseBuildDirectory(
-            new File("${buildscript.sourceFile.parent}/../../.."), rootProject.name, project
-    )
+    def checkoutRoot = new File("${buildscript.sourceFile.parent}/../../..")
+    init.chooseBuildDirectory(checkoutRoot, rootProject.name, project)
     // https://youtrack.jetbrains.com/issue/KT-58223
-    def kotlinDir = new File(System.getenv("OUT_DIR"), ".kotlinBuildSrc")
+    def kotlinDir = new File(System.env.OUT_DIR ?: checkoutRoot, ".kotlinBuildSrc")
     project.setProperty("kotlin.project.persistent.dir", kotlinDir.absolutePath)
 }