ctdb-readonly: Avoid a tight loop waiting for revoke to complete

ctdb-readonly: Avoid a tight loop waiting for revoke to complete

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12697

During revoking readonly delegations, if one of the nodes disappears, then
there is no point re-trying revoking readonly delegation.  The database
needs to be recovered before the revoke operation can succeed.  So retry
only after a grace period.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Autobuild-User(master): Martin Schwenke <martins@samba.org>
Autobuild-Date(master): Fri Mar 17 14:05:57 CET 2017 on sn-devel-144