ceph: fix race between cap issue and revoke

If we receive new caps from the auth MDS and the non-auth MDS is
revoking the newly issued caps, we should release the caps from
the non-auth MDS. The scenario is filelock's state changes from
SYNC to LOCK. Non-auth MDS revokes Fc cap, the client gets Fc cap
from the auth MDS at the same time.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Sage Weil <sage@inktank.com>