Update launch-node script.

* Update credential paths in launch README.
* Add puppet environment command line option to launch-node.
* Invoke install_puppet.sh from launch-node.

Change-Id: I11a326d4be2274fcecb1a58a32c8962b36af24a8
Reviewed-on: https://review.openstack.org/19000
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins