librbd: add new lock_get_owners / lock_break_lock API methods

librbd: add new lock_get_owners / lock_break_lock API methods

If the client application supports failover, let the application
force break the current lock and blacklist the owner. This is
required in case the current lock owner is alive from the point-of-view
of librbd but failover was required due to a higher level reason.

Fixes: http://tracker.ceph.com/issues/18327
Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit 9a5a8c75a025143cee6f92f3dbc3a12f2b6a9ad7)