@edunham is switching all of our Mac builders to OS X 10.11. Because our Salt states change the underlying system in various ways, they could be affected by the specific OS version, so we should test using the same version.

In order to this, we should set the osx_image key in the .travis.yml file for any Mac builders. We'll need to set the value to either xcode7.3 or xcode7.2 to get OS X 10.11 - @edunham @larsbergstrom do you know which Xcode we install? (That should also get documented on the wiki.)