When trying to identify various RedHat releases, RHEL was not being
picked up as a centos release because the Oracle Linux regex was too
permissive: it would match any release name with '<something> Linux
Server release' in the name. By being more restrictive with the Oracle
regex, RHEL is now properly identified.
I don't know why the Oracle regex used such a permissive matcher for the
name but it still passes all the tests by replacing it with the word
'Oracle'.
Fixes#436
