Moving health history from health to agent.

Agent will need to take into account other stuff.
Removing go/vt/vttablet, merging it into tabletmanager.

Still a bunch of stuff to clean up.
Merge branch 'replication' of github.com:youtube/vitess into replication
Moving HealthRecord to healthcheck.go
Cleanup up import.
Moving actor into its own library.

That way vtaction doesn't link with tabletmanager any more.
Merge branch 'ssrepl' of github.com:youtube/vitess into ssrepl
Fixing integration tests with new states.