Add Kubernetes config for vtgate, and a sample vtgatev2 client.

@alainjobart @shrutip 

This is now an end-to-end example of an unsharded keyspace with a client. We can later build on this base with other articles that explain how to do initial sharding, resharding, etc. with concrete instructions that refer to this setup.

Currently the client.py requires a local hack in vtgate_cursor.py which I am not committing. Basically I disabled the sanity checking based on reading the topology from zkocc because I don't have any zkocc running. I will talk to @shrutip about fixing this in the right way.