Fix fix_test_cases.py when a test didn't even run, where returncode == None.
Fix fix_test_cases.py when a test didn't even run, where returncode == None.

fix_test_cases.py was misinterpreting returncode == None as success, making it
unable to trace the test cases that didn't even start since it didn't realize
they were failing.

R=csharp@chromium.org
BUG=

Review URL: https://codereview.chromium.org/14296010

git-svn-id: d5a9b8648c52d490875de6588c8ee7ca688f9ed1@194380 0039d316-1c4b-4281-b951-d872f2087c98

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py