During login creating the connection to Wayland server may take longer
than 1 second (KWin busy, high CPU and IO load, ...) causing
WaylandConfig to time out and leave the backend in an inconsistent
This patch increases the timeout to 3 seconds and sets the overall
backend status to invalid if connecting to Wayland server times out.
This will abort the pending KScreen operation and prevent it from
interacting with the broken backend. The next KScreen operation
will try to set up the backend again, hopefully successfully this time.