ctdb-locking: Reduce logging in case of contention

ctdb-locking: Reduce logging in case of contention

Currently, every lock helper will log a message if it cannot get a lock.
This can spam the logs and overwhelm syslog if there are hundreds of
lock helpers waiting for contended record.

Instead keep track of the record for which we have already logged once
with specific timeout interval.  If we get timeout interval larger than
the previously logged interval, then log again once.  This will reduce
the amount of logs for contended records to a single log entry per 10
seconds per record.

Signed-off-by: Amitay Isaacs <amitay@gmail.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>