Only store the SVN revision in the summarized results if we're on a builder

Only store the SVN revision in the summarized results if we're on a builder
https://bugs.webkit.org/show_bug.cgi?id=76976

Reviewed by Dirk Pranke.

This shaves another ~130ms off the single test run-webkit-tests runtime.

* Scripts/webkitpy/layout_tests/controllers/manager.py:
(summarize_results):
* Scripts/webkitpy/layout_tests/controllers/manager_unittest.py:
(ResultSummaryTest.get_result):
(ResultSummaryTest):
(ResultSummaryTest.get_result_summary):
(ResultSummaryTest.get_unexpected_results):
(ResultSummaryTest.test_no_svn_revision):
(ResultSummaryTest.test_svn_revision):
* Scripts/webkitpy/layout_tests/port/base.py:
(Port.use_trac_links_in_results_html):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106035 268f45cc-cd09-0410-ab3c-d52691b4dbfc