Do not install the repo on Amazon Linux

As discussed in https://github.com/theforeman/puppet-passenger/pull/10,
Amazon Linux without lsb installed reports 3.4.48-45.46.amzn1.x86_64 as
operatingsystemrelease. This matched on the old regex while it's based
on EL6 and thus not need it.

One issue we could run into, is what Amazon Linux 5.x is released, but
I hope that by that time, we no longer support EL5 and can drop this
whole repo part.