(maint) Handle Fedora as a proper Redhat variant

The refactor of the operatingsystem fact in ec2bac8 split up fact
resolution but removed the strict ordering of the resolution method.
Fedora has /etc/redhat-release present which caused the redhat fact to
take precedence, but the release string was not matched. The behavior of
the redhat fact defaults to `redhat` if no exact version was matched.
Since the fact was resolved, a lower resolution fact could not be used

This commit adds fedora as a recognized release string so the redhat
resolution behaves as expected.
Merge pull request #502 from adrienthebo/maint-fedora_operatingsystem_fact

(maint) Handle Fedora as a proper Redhat variant