Sync service and systemd modules from oslo-incubator

This patch make systemd know when neutron-service was started. This is
needed in HA environment, previously systemd returned success even
before neutron-server was able to handle requests.

Current oslo-incubator commit on HEAD:
b7ad6ddab8b1d61bf4f52ccaa461a9d68809747b

Implements: blueprint service-readiness
Change-Id: Ic9e4abd11b614a896fbd7454b9a604a69a248d0f
Merge "Sync service and systemd modules from oslo-incubator"