Make os-availability-zones know about cells

This removes the direct-to-object listing of Service objects by the
availability zone routines. Instead, it implements a cell-scanning
approach in HostAPI and uses that for consistent behavior.

The modified behavior of service_get_all() in HostAPI was originally
in another patch, but is moved here because of dependency sequencing.
The HostAPI patch later in this series uses this as well.

Related to blueprint cells-aware-api
Change-Id: I65c2b436bef8837c0e10a5e502e9cd598d9aa0c3

nova/availability_zones.py

@@ -120,8 +120,12 @@ def get_availability_zones(context, get_only_available=False,
         :param with_hosts: whether to return hosts part of the AZs
         :type with_hosts: bool
     """
-    enabled_services = objects.ServiceList.get_all(context, disabled=False,
-                                                   set_zones=True)
+    # NOTE(danms): Avoid circular import
+    from nova import compute
+    hostapi = compute.HostAPI()
+
+    enabled_services = hostapi.service_get_all(
+        context, {'disabled': False}, set_zones=True, all_cells=True)
 
     available_zones = []
     for (zone, host) in [(service['availability_zone'], service['host'])
@@ -136,8 +140,8 @@ def get_availability_zones(context, get_only_available=False,
             available_zones = list(_available_zones.items())
 
     if not get_only_available:
-        disabled_services = objects.ServiceList.get_all(context, disabled=True,
-                                                        set_zones=True)
+        disabled_services = hostapi.service_get_all(
+            context, {'disabled': True}, set_zones=True, all_cells=True)
         not_available_zones = []
         azs = available_zones if not with_hosts else dict(available_zones)
         zones = [(service['availability_zone'], service['host'])