NRWT doesn't store the svn revision in full_results.json on chromium-win

NRWT doesn't store the svn revision in full_results.json on chromium-win
https://bugs.webkit.org/show_bug.cgi?id=64492

Unreviewed.  Just fixing my test-webkitpy regression.

Fix the unit tests.  Unfortunately scm does not use a filesystem
object so we can't control the result of detect_scm_system.
When detect_scm_system would fail, we would log, which would
cause all passing_run integration tests to fail.

* Scripts/webkitpy/common/checkout/scm/scm.py:
* Scripts/webkitpy/layout_tests/controllers/manager.py:
* Scripts/webkitpy/layout_tests/port/base.py:
* Scripts/webkitpy/layout_tests/port/test.py:
* Scripts/webkitpy/layout_tests/run_webkit_tests_integrationtest.py:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@91028 268f45cc-cd09-0410-ab3c-d52691b4dbfc