Hopefully this will allow the Zuul "Depends-On" thing to work better.
Adopting the solution developed by Doug Wiegley for LBaaS:
c61f920f2a54fd829ee37484b3743ab77b909847 and then shamelessly stolen
from armando-migliaccio here: If358edd5cf34fd63b508dc089615bf19d59ee334
Change-Id: I69c53bb2098b30927726e03c6c492a2fb58d4cc2