Make tests more robust (again)

- Kill Xephyr if qtile doesn't start

- Wait for Xephyr to come up or for Xephyr process to terminate (possible cause for hang if Xephyr comes up, but with wrong DISPLAY or xcb problem)

- Wait for qtile to respond or error out using pipes (possible cause for hang if qtile gets caught in a loop before able to respond to status() call)

- If there are terrible problems in waiting for qtile/Xephyr to launch or error, set a sufficiently long (10 sec) timeout

- Add short sleep after rotate and resize xrandr commands (I've seen these tests fail randomly before, hopefully this helps that)