Replace print statements with logging using mozlog

@whimboo 
This is to fix #26 
Given that 'mozmill_automation' is used as prefix for each and every output to stdout and stderr, I would suggest that we reduce this a bit. Given that our scripts are not an API other tools can make use of, I would even use ` ` for the name. That way we have a similar output like [mochitests](https://tbpl.mozilla.org/php/getParsedLog.php?id=49867779&tree=Mozilla-Aurora) on TBPL.