[Qt] Fix test_build_check for Qt on Mac after r148075.
https://bugs.webkit.org/show_bug.cgi?id=115038

Reviewed by Csaba Osztrogonác.

* Scripts/webkitpy/layout_tests/run_webkit_tests_integrationtest.py:
(RunTest.test_build_check):
    run-webkit-tests is supposed to fail, if it is run on a different
    platform than specified on the command line.
    However, Qt allows exactly this for Qt-platforms to allow comparing
    of test results of different baselines.
    Before r148075 "chromium-linux-x86" was used for testing.
    This patch changes the port_name to gtk when running the test on mac.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148971 268f45cc-cd09-0410-ab3c-d52691b4dbfc