vtgate v3: select plans
vtgate v3: more formal tests
vtgatev3: Gate* -> VTGate*
vtgate v3: wire plan building into vtgate
vtgate v3: add forgotten planner.go
parser: AND has higher precedence than OR
vtgate v3: add tests for or clauses
vtgate v3: make code reusable to prep for dmls
vtgate v3: update plans
vtgate v3: plans for delete
Refactoring rebuilding of keyspace.

So it's more efficient, and can support my next changes
(making ServedTypes per-cell).
Remove obsolete zk Docker example.

The useful parts of the zk Docker example have been absorbed into the
Kubernetes example. The Docker-only version is now broken anyway and
there's no point in fixing it since we're not planning to flesh out the
rest of Vitess in Docker-only mode.
vtgate v3: drop keyspace_id col & add IsAutoInc.

We're going to see if keyspace_id column based sharding
can be deprecated in favor of an on-the-fly hash based
sharding which achieves the same thing.
Also, we should support auto-inc through lookup so we
can generate systemwide unique ids for our keys.
Add a mechanism to log private data from exceptions and use case for bind_variables.
First part of per-cell horizontal sharding support.

Still needs:
- disabling query service on sources.
- unit tests for shard methods.
Merge branch 'master' into replication
More coverage in this test case, better checks of the queries.
Merge branch 'master' into resharding
Merge branch 'master' into replication
Adding unit test for UpdateServedTypesMap.