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
I agree with you  that this should me more user friendly. I will think for other ways to make this more cleaner. In the meantime here is the run on Jenkins: with this patch http://selenium.qa.mtv2.mozilla.com:8080/view/Marketplace/job/marketplace.dev.mobile.saucelabs.appium_run/9/HTML_Report/