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)
Add short sleep after rotate and resize