Only install the passenger repository for some OSs

mod_passenger is available in Fedora >= 17 and EPEL6. This means we only
have to install the extra repository for Fedora < 17 and EL5.

This should fix https://github.com/theforeman/puppet-passenger/issues/1
Strings with variables should use double quotes

This bug caused failures on el5 systems.
fixes #2342 converting to ::osfamily to support redhat based distros