<install> bind_key; preflight checks; docs

* added some preflight sanity checks like "is this RHEL 6?"
* compressed some verbose code defining yum repos
* after some research, discovered that the bind key is not half of a
keypair and can be set arbitrarily; re-enabled that ability.
<install> use 2.0 beta channels from RHN
Merge pull request #111 from sosiouxme/enterprise-2.0

improvements + beta channels