Add service_name parameter to neuron::server class

Allow for customizing the name of the neutron-server service.
The use case here is for organizations that build their own
OpenStack packages, and the service names may differ slightly
from the upstream distro defaults.

Change-Id: If539c51279a8a675e40e356fb4445b6324b75936
Merge "Add service_name parameter to neuron::server class"