I would be tempted to just try to collect both and set them as different facts.

split it into two functions, get_redhat_release and get_os_release. and
maybe make get_distribution just pick whichever is set for distribution

redhat-release.distname=
redhat-release.version=
redhat-release.dist_id=
redhat-release.version_modifier=
os-release.pretty_name=
os-release.name=
os-release.id=