Replace deprecated GoogleCredential with new lib
This PR also introduced a CredentialsBundle class to carry
HttpTransport and JsonFactory object which are needed by
most of the GCP library to instantiate client.
* Move terraform and kubernetes folder to be under proxy
There is no reason for them to be under proxy/src/... any more now that
we have a Gradle-idiomatic folder structure.
Our CI (Travis & Kokoro) runs "gradle build", so we need to make
sure that all tasks used in the release process are called during
the build so that breakage can be caught earlier.
In order to stage the GAE folder we need gcloud to be present.
Therefore the Travis config is changed to install gcloud.
See: https://gist.github.com/mjackson/5887963e7d8b8fb0615416c510ae8857
