Make nova.service get service through conductor.

Update nova.service to get a service record through the conductor API.
If a service has been marked as not having db access, a remote conductor
method will be invoked to get the service record.

Part of bp no-db-compute.

Change-Id: Ib701b1111eb4532c7a31d0099b7cb8c01def1935
Merge "Make nova.service get service through conductor."