- also allows it to sync multiple hosts

- adds _grpc_ensure_gcloud_ssh that creates the ~/.ssh/gcloud_compute_engine
  key file if it does not exist

- update all the grpc_** commands that use ssh to call this

Adds a command for triggering a pull of the latest built docker images.
	Change on 2015/01/09 by temiola <temiola@google.com>
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=83641150