Add a new compute API method for deleting retired services

Services and related compute nodes cannot currently be deleted
from the command-line.  If a node is retired, the service list
will continue to show the retired services.

A delete service REST method has been added to the compute
APIs to support the command-line removal of retired services.

Blueprint: remove-nova-compute
Change-Id: I655a7f818bb59c8971feb5841feeefafc3a4580a
Flags: DocImpact
Merge "Add a new compute API method for deleting retired services"