Reformat openstack-common.conf

Use the new 'module' option in openstack-common.conf which is a
multi-string option, allowing each module name to be placed on a
separate line.

This makes it much easier to review changes to the modules list.

Change-Id: I218601a3720287071f05b9f2f624c1de4442d34f
Merge "Reformat openstack-common.conf"