RedHat Network fixes and documentation

- Add a rhn_config parameter for non-CentOS systems that need the RHN configurations in rhn.repo
 - Remove mention of rhnrelease (unused) in favor of typerelease
 - Set default of typerelease to $release in repo.pp (as described in comments)
 - Document using the type parameter for rhn repos
 - Set default http_proxy and https_proxy to ' ' to workaround bug http://projects.puppetlabs.com/issues/19848
 - Update README.redhat.markdown and README.markdown (including examples)
 - Clean up lint errors