Adding a strategy to not set SourceShards with the workers.

Will be used for running the worker repeatedly.
Next phase on the RPC unit tests. Still need to write 50% of the test cases.
More test cases.
Finishing the tests.
Returning connection errors separately for streaming calls in tm.
Merge branch 'replication'
Factoring out some code.
Adding TeeLogger. Using it in vtowrker.
StreamExecute waits for first packet before returning error

StreamGo doesn't immediately return an error if a send fails.
So, there's no direct way of finding this out without trying to
fetch the first value from the channel.
Merge branch 'suguwork'
Adding a ResfreshState RPC call, and making ping a no-op.
Merge branch 'master' of github.com:youtube/vitess
Fixing a couple test values that were wrong.
Fixing Ping's disappearence.
First pass at Docker support.
Agents now tee logs to local and remote.

And a few related fixes. Still need some work on using the loggers.
tabletserver: StreamExecute refactor
Using context in tm RPCs.
Fixing unit test.
tabletserver refactor: move ddl functions