Adding per-cell TabletControlMap, to replace BlacklistedTabletMap.

This is part of resharding refactoring. Next is per cell MigrateServed{Type,From}.
Merge branch 'master' into replication
Now supporting MigratedServedFrom per cell.

And removing the --skip-rebuild flag. Part of the resharding refactoring.
Adding SetKeyspaceServedFrom manual override command.

Part of the resharding changes. This should complete the vertical split changes.
Fixing ETA computation for clone workers.
Merge pull request #104 from youtube/replication

Implement the fixes for resharding for vertical splits.