Make os.services.update work with cells

In the nova.api.openstack.compute.contrib.services:

 * Make update (enable/disable) service work

In nova.compute.api.api.HostAPI:

 Add - service_update - Used by openstack api's services.py

In nova.compute.api.cells_api.HostAPI:

 Add - service_update - Used by openstack api's services.py

In cells:

 * Increase API version from 1.6 to 1.7
 * Add service_update

Fixes bug #1150499

Change-Id: I5651bd5bc328692df82f4d9da27d390a8c95e03f
Merge "Make os.services.update work with cells"