Add service_create to conductor.

This patch adds the service_create method to the conductor service.  It
also updates nova.service to use it.  When a service has been marked as
not using the db, it will invoke a remote conductor method to create the
service record.

Part of bp no-db-compute.

Change-Id: Ie1f2db96d3134b0e30230565e5c000c416ea73d5
Merge "Add service_create to conductor."