Uplift changes for Bug 925398 (includes Bug 945284, Bug 947001)

To help keep our changes up-to-date and to ease uplifting patches later, I'm uplifting the major changes made last week to gaiatest to v1.3. This rolls up the follow up patches (like removing gaia-ui-tests from allow_failures in .travis.yml) into one one PR.

I've tested this locally against my phone and desktop b2g and it works. It should pass Travis and we should be able to land it without issues.