RPM Support

In Fedora 30, Zchunk metadata is going to be present alongside with older compression formats.

Pulp should ignore and not sync this metadata, in order to avoid creating a potentially bad repo at publish time.
Scenario for a bad repo:
- create repo and sync from a remote repo with zchunk metadata
- make any content changes to a repo , e.g. remove/add packages
- published a repo
- zchunk metadata is published as-is without any modifications to it (even though content in a repo changed) -> clients which use zchunk metadata will get incorrect data about the content in a repo.

Repo with this new metadata type: http://mirror.vutbr.cz/fedora/development/rawhide/Everything/x86_64/os/