Updated openstack/openstack
Project: openstack/sahara  f3d6f2a69239a43b36082d59a66cfe21018eddc1

Update links for plugin images

* update link for vanilla images
* update link for hdp images
* small doc refactoring

Change-Id: Ie2d47e57238d00887be4df29f3e2e75b218b8a35