Add with_compute_node to service_get()

Right now, a service_get() call cannot joinedload the compute_node
attribute. This means anything that needs that data has to trigger
a lazy-load. A subsequent change will depend on this.

Related to blueprint compute-manager-objects-juno

Change-Id: Ie537f30374280203ea153230cfa1a7aecfa5b891
Merge "Add with_compute_node to service_get()"