Enable rowcache in Kubernetes example.

Without it, we can't do ApplySchemaShard -simple, because the replicas
will never notice the new schema and will fail to build query plans.
Add Kubernetes config for vtgate, and a sample vtgatev2 client.
Use vitess/base Docker image for client commands.

Instead of running as root with vitess/root. The user shouldn't need to
download any additional image since vitess/root has vitess/base as a
dependency.
Read topology from vtgate.

This is a temporary work-around until the VTGate V2 client is
topology-free.
Merge pull request #140 from youtube/docker

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