Fix T104 for scenario test subdirs

This commit fixes the T104 hacking check to handle subdirs in the
scenario tests. Previously the check assumed that all the scenario
tests were in the scenario dir. However, this isn't necessarily the
case. For example, the heat scenario tests are all in the path:
tempest/scenario/orchestration which means they were excluded from
the T104 check. This commit fixes the oversight and adds unit tests
to cover this condition.

Change-Id: I42d7f22f6194f624f8488493de29e60ff19d211a
Merge "Fix T104 for scenario test subdirs"