Bump grenade master to use stable/havana.

Now that we have cut Havana it is time to move on and use
it (instead of Grizzly) for forward facing Icehouse testing.

This is holding up Nova migration compaction at the moment.

Change-Id: Ib64dafbd3aeb968fb71752a5a26fad105045f5f8
Merge "Bump grenade master to use stable/havana."