Services were being passed as a JSON list, then iterated over in the
neutron-server container's extend_start.sh script like this:

['neutron-server'
'neutron-fwaas'
'neutron-vpnaas']

I'm not actually sure why we have to specify services explicitly, it
seems liable to break if we have other plugins that need migrating.

Change-Id: Ic8ce595793cbe0772e44c041246d5af3a9471d44