smbtorture: add test "open-brlock-deadlock"

smbtorture: add test "open-brlock-deadlock"

smbtorture reproducer for bug 15767. As it needs a very specific setup that
can't easily be done in selftest, the test is only executed when manually called
with

  --option=torture:open_brlock_deadlock_timemout=SEC

To prepare the setup for the test set:

  tdb_hash_size:locking.tdb = 1
  tdb_hash_size:brlock.tdb = 1

and remove both tdb from disk which is needed so the TDBs get recreated with the
new hash_size.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15767

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>