Adding a helper to retry an action until a timeout.

Usefull to write tests that wait for something.
I wish there were better closures in python...
Fixing comment.
Moving a parameter up so there is no conflict.
Fixing another comment.
Merge branch 'master' of github.com:youtube/vitess
Only rebuild serving graph for serving types.

During tablet health check.
Merge branch 'master' into bson