Searching based on class is used in many tests, searching by class, not
only by name in wait_for_window will allow to reduce code duplication.
While at it, improve it additionally:
- avoid active waiting for window and use `xdotool search --sync` instead
- return found window id
- add wait_for_window_coro() for use where coroutine is needed
- when waiting for window to disappear, check window id once and wait
for that particular window to disappear (avoid xdotool race
conditions on window enumeration)
Besides reducing code duplication, this also move various xdotool
imperfections handling into one place.
f1621c01e9