RPM Support

During copy or sync operation after a migration from pulp 2, it is possible to get a conflict for advisories.

pulp_rpm.app.exceptions.AdvisoryConflict: Incoming and existing advisories have the same id and timestamp but different and intersecting package lists. At least one of them is wrong. Advisory id: FEDORA-EPEL-2019-927a9446df

Because of Pulp 2 filtering out packages from pkglist when they are not in a repo and some advisories referring to packages which are not in a repo, it is not possible to migrate a full original advisory from Pulp 2 to Pulp 3.
Such advisory will have a subset of packages from the original advisory pkglist.
E.g. FEDORA-EPEL-2019-927a9446df` from EPEL7 repo refers to a binary and to a source rpm (php-robrichards-xmlseclibs-2.1.1-1), in EPEL repo there are only binary ones present, so such advisories will always cause a conflict after migration.

A workaround (not an easy or straightforward one) for users is to remove such advisories from Pulp 3.

Proposed solution: Do not raise a conflict when one pkglist is a subset of another, just pick the one with superset.