ctdb-locking: Add per database queues for pending and active lock requests

ctdb-locking: Add per database queues for pending and active lock requests

This avoids traversing a single pending queue which is quite expensive
when there are lots of pending lock requests.  This seems to happen
quite a lot on a loaded cluster for notify_index.tdb.

Adding per database queues avoids the need to traverse pending queue
for that database if there are already the maximum number of active
lock requests.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Reviewed-by: Volker Lendecke <vl@samba.org>
Autobuild-User(master): Volker Lendecke <vl@samba.org>
Autobuild-Date(master): Mon Aug  4 20:23:45 CEST 2014 on sn-devel-104