Minor launch documentation improvements.

* launch/README: Demonstrate use of the nova client's image-list
and flavor-list features, to assist in selecting/confirming image
and RAM choices for passing to launch-node.py. Also improve the
section headers and add a section about activating the Puppet agent
on non-Jenkins-slave servers.

* launch/launch-node.py: Upon successful completion, display
parameters useful for subsequent DNS assignments.

Change-Id: I0defc62434ab2f60b23afe2048e8093614ca49ca
Reviewed-on: https://review.openstack.org/20923
Reviewed-by: Khai Do <do.khai@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins