Fix 'File Dialog' issues with test playback on OsX
On OsX, when playing tests, any tests with file dialog exhibited following issues:
- With Qt 4, the test would segfault randomly
- With Qt 5.7, the test would deadlock quite reliably.
In both cases, it seemed something to do with the what causes the
dialog's event loop to close since I could narrow it down
to pqFileDialog::selectFile
call to QDialog::accept
.
Instead of explicitly doing that, we now trigger a "click" on the OK button. This seems to address the issue entirely. Is also consistent with how other modal dialog behave during test playback.