Lock-related infrastructure cleanups.

Add a "rejester global_lock" command which prints out who has the
global lock; "rejester global_lock --purge" force-clears it.

Clarify that the atime and ltime parameters to Registry.lock() are
*seconds*, and fix all of its callers that try to get 10,000-second
locks to just use the default times (atime=30s, ltime=5s).  Allow a
caller to pass the lock token and use the (Worker) worker_id explicitly
at most call sites.

Remove the separate Registry.worker_id and its maintenance atexit()
job.

Fix the remaining script invocations to use the pyredis callable script
mode, and change all of the key-name calculations to run at the Python
level.