Adding per-cell TabletControlMap, to replace BlacklistedTabletMap.

This is part of resharding refactoring. Next is per cell MigrateServed{Type,From}.
Merge branch 'master' into replication
Now supporting MigratedServedFrom per cell.

And removing the --skip-rebuild flag. Part of the resharding refactoring.
Adding SetKeyspaceServedFrom manual override command.

Part of the resharding changes. This should complete the vertical split changes.
Fixing ETA computation for clone workers.
Add unit tests for VTGate shard_conn reconnect
Merge pull request #104 from youtube/replication

Implement the fixes for resharding for vertical splits.
Stopping replication before copying data in clone workers.

Then we change the type of the servers back to 'spare' and restart replication.
That way when they catch up (and if healthcheck is enabled) they
come back to serving state.
Merge pull request #106 from youtube/replication

Stopping replication before copying data in clone workers.
Also listening on abort channel for writes in workers.

That way if there is an error, we don't get stuck forever.
Merge branch 'master' into replication
Merge pull request #107 from youtube/replication

To fix a case where the worker hangs.
Merge pull request #105 from youtube/liguo

Add unit tests for VTGate shard_conn reconnect
Fixing a flaky test.
Improve VTGate reconnection logic.
It refreshes endpoints before every connection.
First pass at a vtworker test.
One step further in the unit test.
Fix package comments for vtctl.
Remove -follow flag from mysqlctl, to be replaced by mysqlctld.
Create mysqlctld service for remote mysqlctl actions.

This is intended for use internally by vttablet, in cases when it cannot
directly access the mysqld process because they are running in separate
cgroups (containers). Since vttablet and mysqld can share files, many
actions can still be done directly by vttablet. However, starting and
stopping mysqld must be done from within mysqld's cgroup, so these
actions are executed remotely by mysqlctld.