[Android] Add the instrumentation test for runtime client.

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

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

For shared client test:

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