add RNTester to ci (facebook#19673)

Summary:
* Current ci is missing an important part to test the whole part. With this we can make sure the js and android part compiles.
* Ensure the current android proguard rules is okay.

The `my-release-key.keystore` is just a copy of debug.keystore in `react-native/keystores`.
Pass all ci.
none
 [GENERAL] [ENHANCEMENT] [CI] - Add RNTester to ci
Closes facebook#19673

Differential Revision: D8435419

Pulled By: hramos

fbshipit-source-id: d3d92a5d1b8477c1f298643cc96695769e5c93ea

Author: gengjiawen

.circleci/config.yml

@@ -558,6 +558,12 @@ jobs:
       - run: *run-android-unit-tests
       - run: *run-android-instrumentation-tests
 
+      # Build Android RNTester
+      - run:
+          name: Build Android RNTester
+          command: |
+            ./gradlew RNTester:android:app:assembleRelease
+
       # Collect Results
       - run: *collect-android-test-results
       - store_test_results:

RNTester/android/app/build.gradle

@@ -81,7 +81,7 @@ def enableSeparateBuildPerCPUArchitecture = false
 /**
  * Run Proguard to shrink the Java bytecode in release builds.
  */
-def enableProguardInReleaseBuilds = false
+def enableProguardInReleaseBuilds = true
 
 android {
     compileSdkVersion 26

RNTester/android/app/gradle.properties

@@ -2,6 +2,6 @@ android.useDeprecatedNdk=true
 org.gradle.parallel=true
 org.gradle.configureondemand=true
 MYAPP_RELEASE_STORE_FILE=my-release-key.keystore
-MYAPP_RELEASE_KEY_ALIAS=my-key-alias
-MYAPP_RELEASE_STORE_PASSWORD=*****
-MYAPP_RELEASE_KEY_PASSWORD=*****
+MYAPP_RELEASE_KEY_ALIAS=androiddebugkey
+MYAPP_RELEASE_STORE_PASSWORD=android
+MYAPP_RELEASE_KEY_PASSWORD=android