Using context in all the topo server lock methods.

So we can remove timeout and interrupted.
Removing global wrangler interrupted channel, now just
cancelling its context.
Fixing capitalization of error messages.
Merge branch 'master' into replication
Fixing context path.
Removing dummy context.
Few fixes after review, and fix the tests.
Caling the cancel() function for context more.

Even if err != nil.
Merge pull request #242 from youtube/replication

Replication