Improve OpenHelp test

The test was a bit flaky. Improve it by changing the last click. Instead
of clicking inside the help browser, make sure that the help is displayed
when clicking a question mark on an object (a cone source in this case).

Change-Id: I415c803ef5e74047b7a855a092bf3967a09fd0d9
Merge topic '14720-RemoveQtWebkit' into next

aac9c95f Improve OpenHelp test