Clean up slow HTTP tests on GTK platform

Clean up slow HTTP tests on GTK platform

Rubber-stamped by Martin Robinson.

Skip the HTTP tests that take half a minute to run, most oftenly failing
as well. These tests only extend the overall testing time.
Also group the tests failing due to missing authentication handling in DRT,
missing multipart/x-mixed-replace support in libsoup and open a new bug
for the failing http/tests/plugins/plugin-document-has-focus.html test.

* platform/gtk/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121693 268f45cc-cd09-0410-ab3c-d52691b4dbfc