Add api.python.failing_step
Add api.python.failing_step

This is a replacement for repetitive pattern and gets correctly
recognized as failing in test expectations.

BUG=none

Review URL: https://codereview.chromium.org/494073002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@291121 0039d316-1c4b-4281-b951-d872f2087c98

luci/recipes-py,luci/recipes-py,shishkander/recipes-py,shishkander/recipes-py