Agents now tee logs to local and remote.

And a few related fixes. Still need some work on using the loggers.
Using context in tm RPCs.
Fixing unit test.
vtctl server now tees the logs to console and remotely.
Forwarding logging for [multi]{snapshot,restore}.
Merge branch 'master' into replication
Merge branch 'master' of github.com:youtube/vitess
Merge branch 'master' of github.com:youtube/vitess