Implement semaphore mechanism to assure crontab calls stacking up.

[cttyler]

Implement a semaphore mechanism in the scripts to assure crontab calls, which run every minute, don't stack up if for some reason the usually quick commands it calls take more than a minute to run.

[jdputsch]

@cttyler : quick questions/statements:

1. For monitor_metrics.sh were you picturing a lock at the level of monitor_metrics.sh or at the level of the individual functions in that script?
2. I would assume monitor_metrics.py and/or it's wrapper would just be locked at the script level.

I've done this locking for shell scripts in the past, and it's quite simple to do the locking at the script level, quite willing to conribute something here.

Jeff.