Adding neutron_service_provider type

Currently, in the neutron server config, multiple keys, each named
"service_provider", must be specified in the "service_providers" section.
The current implementation comma separates each value mapped to a
single "service_provider" key. The ini provider used does not allow for
the existence of multiple same key, different value pairs. This
workaround resolves the issue for the service provider.

Change-Id: I0798add40fe50a13180d8092b37056937496c87d