android-interop-testing: resolve build warnings (#6870)

Suppressed compiler warnings caused by protobug-javalite and errorrprone warnings from grpc-interop-testing + "throw-in-finally".

android-interop-testing/build.gradle

@@ -87,4 +87,14 @@ task checkStyleTest(type: Checkstyle) {
 
 project.tasks['check'].dependsOn checkStyleMain, checkStyleTest
 
+import net.ltgt.gradle.errorprone.CheckSeverity
+
+tasks.withType(JavaCompile) {
+    options.compilerArgs += [
+            "-Xlint:-cast"
+    ]
+    // Reuses source code from grpc-interop-testing, which targets Java 7 (no method references)
+    options.errorprone.check("UnnecessaryAnonymousClass", CheckSeverity.OFF)
+}
+
 configureProtoCompilation()

android-interop-testing/src/main/java/io/grpc/android/integrationtest/InteropTask.java

@@ -53,6 +53,7 @@ final class InteropTask extends AsyncTask<Void, Void, String> {
     tester.setUp();
   }
 
+  @SuppressWarnings("Finally")
   @Override
   protected String doInBackground(Void... ignored) {
     try {