This should make it easier to have a common configuration between local
docker-compose environments and the config for the modularity.fic.org
cloud node.
koji.read_config() filters out configuration options it doesn't know
about silently. Currently this is about the keytab, principal, ccache
options. The latter may be needed e.g. in Docker containers which
currently(?) can't use Linux kernel keyrings and need the credential
cache to be a normal file.
Before this, we were consulting pkgdb to see if the given user was the
maintainer of any packages.
That mostly works... but technically, we want to consult FAS to see if
the user is in the packager group.
We found this when @mprahl was unable to submit builds to rida. I added
him to the packager group, but nothing changed! (As written, he had to
actually own a package).
This change fixes all that so that we query FAS instead of pkgdb.
Tests are added.
