Deadlocks qr8mb ehn

@kbarrette 

Add retry to the `clear_lock!` instead of fail immediately.  The attempt is hardcoded to 10 tries since that is what the `self.reserve` is set to. 

~~Also fixes a bug where the retry count was 1 more than the max retry.~~ Max retry is fine, it is in addition to the first run.
It was added as convenience scope for the rspec to inspect, called from `self.clear_locks!`