Show error if delorean-deps.repo/delorean.repo files are missing
Show error if delorean-deps.repo/delorean.repo files are missing

If the baseurl config setting is incorrectly set in projects.ini,
build_rpm_wrapper() will fail with a non-descriptive message, usually
a 404 error. This makes troubleshooting complicated, so let's catch
the exception and provide a descriptive error message.

Change-Id: I06c4d50779575d4c3f762694ac313f6934224fac
Story: 182
Task: 463

openstack-packages/DLRN,openstack-packages/delorean,openstack-packages/delorean,openstack-packages/DLRN