Have webkit-patch rebaseline use rebaseline-test-internal

Have webkit-patch rebaseline use rebaseline-test-internal
https://bugs.webkit.org/show_bug.cgi?id=90491

Reviewed by Dirk Pranke.

This lets it handle new files, reduces duplicate code and lays the
groundwork for making rebaseline have a richer interface.

* Scripts/webkitpy/common/net/buildbot/buildbot_mock.py:
(MockBuild):
(MockBuild.__init__):
(MockBuilder.build):
* Scripts/webkitpy/tool/commands/rebaseline.py:
(AbstractParallelRebaselineCommand._files_to_add):
(Rebaseline):
(Rebaseline._builder_to_pull_from):
(Rebaseline._tests_to_update):
(Rebaseline.execute):
* Scripts/webkitpy/tool/commands/rebaseline_unittest.py:
(test_overrides_are_included_correctly):
(test_rebaseline):
(test_rebaseline.mock_builder_to_pull_from):
(test_rebaseline.mock_tests_to_update):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121800 268f45cc-cd09-0410-ab3c-d52691b4dbfc