Improve openstack modules

* Al modules now get their default authentication information from the environment, just like the openstack cli tools do.
* Where possible, objects (volumes, networks, routers, etc.) can be referenced both by name and by ID.
* nova_compute has received a general cleanup, and now accepts its parameters in much more intuitive forms.
* nova_compute now allows vm rebuild
* nova_compute now allows volume attachments.
* cinder_volume allows creation and deletion of volumes.
* quantum is now usable for non-admins (e.g. public cloud users)

This fork request isn't quite ready for merging yet. This merge request is mostly intended to solicit some reviews.