X11 tests for all de/wm

This adds tests for all de/wm combinations, that can be run using the `w` prefix.

Sample runs: `2014-11-14_22-17-28_drinkcat_chroagh_x11test_w` and `2014-11-14_22-17-38_drinkcat_chroagh_x11test_x`.
Yes. I just implemented in the last commit. It's not really that useful as we need to have long sleeps anyway to make sure that the DE/WM has enough time to start (e.g. display splash screen, panels, etc...), but maybe we can save a bit of time...