[1.5] Update automation script to also handle the new application-based structure

Added a check to see if the current path doesn't exist, to update it by including the application name.

Application is already by default firefox, if none provided. I did not add metrofirefox here since we will not use 1.5 for metro.

Performed testruns with both current mozmill-tests and with the new structure patch applied. Both work, please see reports:
http://pastebin.mozilla.org/3318426