[GTK][webkitpy] A huge list of warnings about missing bugs in expectations when running NRWT with WKTR
https://bugs.webkit.org/show_bug.cgi?id=113421

Reviewed by Dirk Pranke.

When running the layout tests with WKTR through NRWT, the GTK port also uses the generic WK2 TestExpectations file.
This file contains a large amount of expectations that are not listing a specific bug modifier, so this produces an
equally large amount of warnings due to the GTK port preferring for every expectation to have the bug modifier present
in the GTK-specific TestExpectations files.

To avoid this only enable the warnings only when not using WKTR.

* Scripts/webkitpy/layout_tests/port/gtk.py:
(GtkPort.warn_if_bug_missing_in_test_expectations):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146998 268f45cc-cd09-0410-ab3c-d52691b4dbfc