Replace glance-api+glance-reg elements with glance:

'glance' element now results in a properly-configured,
working glance service on first boot.

While glance-api and glance-reg may need to be broken
out again in the future, the intention now is to focus
on a working service for an end-to-end PoC.

Change-Id: I4fb1cd5ad6defef5a5c4fddfded46d51e8097b5a