svc_monitor unable to handle empty az list from nova

This fix adds error handling to svc_monitor code. If nova
returns empty az_list or if the call to nova fails for some
reason, svc_monitor will not crash after this fix.

Change-Id: Ib132401d931c763c36c9eca46bfd855663b070b9
Closes-Bug: #1593432

src/config/svc-monitor/svc_monitor/scheduler/vrouter_scheduler.py

@@ -59,11 +59,30 @@ def _get_az_vrouter_list(self):
         az_list = self._nc.oper('availability_zones', 'list',
                                 self._args.admin_tenant_name,
                                 detailed=True)
+        if not az_list:
+            self._logger.log_error("Failed fetching azs from nova")
+            return None
+
         az_vr_list = []
         for az in az_list:
-            if self._args.netns_availability_zone not in str(az):
+            try:
+                # check:
+                # 1. If az is mentioned in config
+                # 2. If the az is enabled & active
+                # 3. If it has any hosts
+                if az.zoneName not in self._args.netns_availability_zone or \
+                   not az.zoneState['available'] or not az.hosts:
+                    continue
+
+                # check if hosts are active & enabled
+                for host,host_status in az.hosts.iteritems():
+                    if (('nova-compute' in host_status) and \
+                        host_status['nova-compute']['available'] and \
+                        host_status['nova-compute']['active']):
+                        az_vr_list.append(host)
+            except Exception as e:
+                self._logger.log_error(str(e))
                 continue
-            az_vr_list.extend(az.hosts.keys())
 
         return az_vr_list