Reviewed by Adam Barth.

        commit-queue should commit rollouts without running tests
        https://bugs.webkit.org/show_bug.cgi?id=38940

        Most of this change is improving our test coverage for the commit-queue.
        The only functional change is removing the --test flag when the commit-queue
        is running in rollouts mode.

        I added test coverage for status updates, and updated the commit-queue status
        messages to distinguish rollout vs. normal landing mode in its empty queue
        and land patch messages.

        * Scripts/webkitpy/tool/commands/earlywarningsystem_unittest.py:
         - Got rid of a bunch of copy/paste code using _default_expected_stderr
        * Scripts/webkitpy/tool/commands/queues.py:
         - Moved rollout patch filtering out of _validate_patches_in_commit_queue
           so that we only have to check if the builders are green in one place.
         - Make the "empty queue" message note which queue it is referring to.
         - Don't pass --text to land-attachment when in rollout mode.
        * Scripts/webkitpy/tool/commands/queues_unittest.py:
         - Update results now that we're testing status updates.
         - Test _can_build_and_test since I made a typo in that call while
           writing this change and the unit tests failed to catch it!
        * Scripts/webkitpy/tool/mocktool.py:
         - Log status updates to make them testable in our unit tests.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@59200 268f45cc-cd09-0410-ab3c-d52691b4dbfc