Clean up PE master setup/up manifests.

This commit cleans up the two manifests that setup a PE master and
configure parts of it for the GCE demo. These were tested with the
included configuration, a centos-6 based GCE instance.
Update README.md for PE Master setup

This commit updates the README to include a quick start guide which
builds a Puppet Enterprise master using the gce_instance Puppet type.
It also provides instructions for using a newly provided manifest
to automate some of the demo configuration necessary, without
requiring any PE knowledge on behalf of the user.