cells: instance can not evacuate in cells

[nail-zte]

There has one api cell and two child cell and four compute nodes,api cell has not compute node. I boot an instance and evacuate the instance, then return error:
[root@apicell ~(keystone_admin)]# nova evacuate test_vm5
ERROR (NotFound): The resource could not be found. (HTTP 404) (Request-ID: req-63786e5b-1199-4e2a-a5c0-a1efde0398a8)

the error log in api cell nova-api.log in:
http://paste.openstack.org/show/482160/

The reason is that nova api in api cell first check compute node nova-compute status before evacuate the instance , it calls db.service_get_by_compute_host function, but the api cell db has not compute node service record. Thus resulting in failure evacuate：
 Caught error: Compute host CL-SBCJ-5-3-4 could not be found

[Sean Dague (sdague)]

This is cells v1 missing functionality, it won't be fixed