Added the ability to manage the nova uid/gid.

Added the ability to manage the nova user and group ids. This is
necessary for users who want to use live migration on NFS, where the
nova uid and gid must be the same on all systems.

Change-Id: I8958c5081afa7ffa73b59fb9a30b63ca725fcc66
Merge git://github.com/puppetlabs/puppetlabs-nova