Comment 10 for bug 1442121

Per discussion on https://review.openstack.org/#/c/289371/8 I think we're going to aim to just catch any exceptions that occur for this bug, and I've opened several other bugs (bug 1626607, bug 1626619, bug 1626630, bug 1626634) to address the wider issue of getting rid of ReST calls from the dependency calculations altogether.