Don't assume processEvents(WaitForMoreEvents) will process timers

The WaitForMoreEvents flag only guarantees that we will process _some_
events -- either if they are in the event queue already, or by sleeping
and then waking up to process an event. This event might be a system
event, not the timer firing, so a single call to processEvents() is
not enough to guarantee that the timer has fired. Instead we do a
Q_COMPARE with a timeout, where we continiously process events until
we see that the timer fired.

Change-Id: I5dc04377f04190f3505be22e877af73d11b7547d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>