Occasionally oslo library usage sneaks in, so add a coding check
that checks for ^oslo\. in requirements.txt. We currently still
use oslo.test, so don't check test-requirements.txt. This should
fail to pass tests until I34357d5a594330d07f5cad372859d98efb5d3fde
merges.
Change-Id: I53108584ee47a7f1b6c7df90c49f95725cec69f9
f4855dd66f