note becmodel version commit in logfile

[smnorris]

For iterative small changes, it would be useful to note exactly what commit generated a given output - something like this: https://stackoverflow.com/questions/14989858/get-the-current-git-hash-in-a-python-script

This is easy enough on my end but applying this in the GTS environment may not work. Maybe just check to see if git is available and if so, note commit as well as version.