Updated protobuf gradle plugin version to 0.8.13. Fixed Android Kokoro's memory issue by forcing to use a new Gradle daemon for building the previous commit.
* added android example running under strictmode to detect grpc clear text network transport
* renamed andriod strictmode example
* use OkHttpChannelBuilder's api to feed with user's own transport executor
* bump gradle and proto-plugin version to match that in master
* add README with a simple demo image
* Update README to use relative link to helloworld
Chengyuan Zhang