Bring automationutils.py up to date with trunk 7ac3f76249e7 (includes the fixes for bug 850681, bug 813577, bug 808410); a=test-only

This updates the file from b1a7fae2cf18 to 7ac3f76249e7:
https://hg.mozilla.org/mozilla-central/log/7ac3f76249e7/build/automationutils.py