Fix examples. (#102)

* Fix ex2 and ex4 builds
* Update unsupported target SDK version.
* Update usage of deprecated API of instrumentation registry.
* Update apk path in tutorial.
diff --git a/examples/ex2_espresso/README.md b/examples/ex2_espresso/README.md
index 03973d1..b43507a 100644
--- a/examples/ex2_espresso/README.md
+++ b/examples/ex2_espresso/README.md
@@ -111,7 +111,7 @@
 
 1.  Install the apk on your phone
 
-        adb install -r ./examples/ex2_espresso/build/outputs/apk/debug/ex2_espresso-snippet-debug.apk
+        adb install -r ./examples/ex2_espresso/build/outputs/apk/snippet/debug/ex2_espresso-snippet-debug.apk
 
 1.  Use `snippet_shell` from mobly to trigger `pushMainButton()`:
 
diff --git a/examples/ex2_espresso/build.gradle b/examples/ex2_espresso/build.gradle
index 64dcdc6..9caf136 100644
--- a/examples/ex2_espresso/build.gradle
+++ b/examples/ex2_espresso/build.gradle
@@ -18,6 +18,7 @@
             dimension "examples"
         }
         snippet {
+            testApplicationId "com.google.android.mobly.snippet.example2.snippet"
             dimension "examples"
         }
     }
diff --git a/examples/ex2_espresso/src/snippet/AndroidManifest.xml b/examples/ex2_espresso/src/snippet/AndroidManifest.xml
index 95ee221..85797ce 100644
--- a/examples/ex2_espresso/src/snippet/AndroidManifest.xml
+++ b/examples/ex2_espresso/src/snippet/AndroidManifest.xml
@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="com.google.android.mobly.snippet.example2.snippet">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
 
     <application>
         <meta-data