Stabilize QQuickTextEdit test

tst_qquicktextedit::remoteCursorDelegate was failing
because the test server served the the remote file too
fast. It seems like the test relied on a slow machine to
run it.
Instead pass the Delay option to make the server serve
the file delayed.

Change-Id: Id99feea07f2da3b2ea0aa6c07e9b548e8f81f18b
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>