Handle the case when tempest fails

Before this change, the errors from tempest run are suppressed
in order to always execute cinderlib tests.

Use the new variable exported by run-tempest instead,
and fail properly if needed.

Depends-On: https://review.opendev.org/720213
Change-Id: Ic1fd6fcc9b9183f195c66f0022e913ae9734c97b
1 file changed