Run application main run loop in color/font dialog test

Run application main run loop in color/font dialog test

In cocoa the timers are associated with main run loop but
the way font and color dialog tests are executed the modal
dialog run loop is only run in cocoa. This causes timers to
not to fire and test cases to hang.

Unfortunately this does not completely fix the test failure
because the QTest::keyClick is not working with cocoa
native dialog helpers and therefore the tests are marked
with QEXPECT_FAIL.

Task-number: QTBUG-24320
Task-number: QTBUG-24321

Change-Id: I88740a20ad2b794b6ca15e1b6455f436ffd39335
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>