Adding Appium support for Saucelabs

Capabilities that we need to run Appium on Saucelabs https://support.saucelabs.com/entries/51370580-Android-Desired-Capabilities

This is for issue https://github.com/mozilla/pytest-mozwebqa/issues/122
Currently  Saucelabs can only run the Mobile Web Application with Appium version 1.2.2 and Android 4.4