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.
Use @var for puppet 3.2 compatibility