Support Oracle Linux 5.x

Oracle Linux 5, also known as Unbreakable Linux is currently
not supported by salt.

This one line fix solves this issue.

For reference, the os info extracted through platform.linux_distribution()
python call:
('Enterprise Linux Enterprise Linux Server', '5.1', 'Carthage')

The os is now reported as part of the RedHat family and the pkg module is now working.