[Android] Add the instrumentation test for runtime client.

This instrumentation test contains the embedded and shared client.
For embedded client test:

    install XWalkRuntimeClientEmbeddedShell.apk
    python build/android/test_runner.py instrumentation \ --test-apk=XWalkRuntimeClientEmbeddedTest -v

For shared client test:

    install XWalkRuntimeLib.apk
    install XWalkRuntimeClientShell.apk
    python build/android/test_runner.py instrumentation \ --test-apk=XWalkRuntimeClientTest -v