Rather than expecting a certain amount of signals to be fired within
a fixed period, check that all the required signals are emitted and
that it doesn't take longer than expected. Use a margin of error to
take into account timers firing later because of high system load.

Change-Id: I7f77d32a9db3d09881eadbd0dfc6b70f62757d09
Reviewed-by: Christian Stromme <christian.stromme@qt.io>