This unit test class relies on calling waitForEventIdle to wait for
UI transitions to complete.  On Windows this is not reliable, due to
VCL's use of PostMessage (Windows message queue) to asynchronously
handle some events such as focus changes.

This issue causes the test to intermittently fail when the dispatcher
for the action the test wants to perform (like closing the print
preview) is not available yet.

 - Change the test code to explicitly wait for the desired dispatcher
   to be available

 - Remove the sleep which was added earlier this year to address this
   symptom in one location

Change-Id: Id701209a28cd0c806ab0a548508d31f9f11211f5
Reviewed-on: https://gerrit.libreoffice.org/29167Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>