[Qt] run-webkit-tests cleanup for parallel NRWT
https://bugs.webkit.org/show_bug.cgi?id=106220

Reviewed by Dirk Pranke.

* Scripts/run-webkit-tests:
(useNewRunWebKitTests):
* Scripts/webkitpy/layout_tests/port/qt.py:
(QtPort):
(QtPort.default_child_processes):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@138951 268f45cc-cd09-0410-ab3c-d52691b4dbfc