Work around for facter bug yielding warnings.

There is a facter bug (http://projects.puppetlabs.com/issues/18429) that
emits warnings on every run.

Could not retrieve selinux: Invalid argument - /proc/self/attr/current

This is a work around for that bug until it can be fixed directly.
Solution from:

http://mattiasgeniar.be/2012/07/31/facterpuppet-could-not-retrieve-selinux-invalid-argument-procselfattrcurrent/