Purge: only check for rpm in directory if there are rpms in commit
Purge: only check for rpm in directory if there are rpms in commit

There are cases where a commit does not have any associated RPM,
such as when it failed to build. In those cases, the check in
is_commit_in_dirs() should return False instead of trying to find
the rpms (which fails).

Change-Id: I3b14d286e09e02c78008818e07153879d16e1cca

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