Handle GRANTED_RES messages more gracefully: Send along a grant cookie

Handle GRANTED_RES messages more gracefully: Send along a grant cookie
to reference the lock, look up the grant cookie when the GRANTED_RES
comes back. Properly handle the case of an error on the grant. Add a
short expiration window so that granted locks are not freed immediately.

Approved by:        dfr (mentor)
MFC after:          2 weeks