Use the repos_base which might have been set to the default value.
Support the Enterprise 1.2 release.

If the CONF_RHEL_REPO points to the os/ subpath of CONF_REPOS_BASE,
we assume Enterprise 1.2 release layout as found on CDN.
Make the baseurl setting logic a bit less verbose.
<install> consolidate yum repo base url
Merge pull request #40 from sosiouxme/support-release-repos

Support release CDN yum repos in addition to puddles