git-logs: Allow use of -c argument

This allows you to run the script without having to input a commit
each time:

usage:
python log_updates.py -c b82541914f989a40ff05fd338ac1b875d873f530

Change-Id: Iad13f99970eaafb4eb59532c4f3ea3842f44a1a5
Merge "git-logs: Allow use of -c argument"