Remove logger.exception from zc.lockfile

Currently the behaviour in zc.lockfile is the log the LockError as an exception.
This causes a lot of small stracktraces in ZODB3 when trying to 'check_blob_cache_size'.
Even if the using product handles the error correctly it still shows up, suggesting a problem.
This seems unwanted behaviour.

So instead of logging it as an exception, I suggest to raise it as a new LockError with the 'pid' added.
And let whoever uses it worry about if they want to log it or not.