apply optimizations via standard method

This addresses the top-level resources in the v2
root view, focusing in order of priority,
reflecting use by the UI.

In several cases get_queryset logic from the view
is moved into the access class.

Most other cases involve adding a straightforward
select_related or prefetch_related entry.

All additional confirmed to be effective with the
django debug toolbar.

awx/api/views/root.py

@@ -167,7 +167,7 @@ class ApiV1PingView(APIView):
                                               capacity=instance.capacity, version=instance.version))
             sorted(response['instances'], key=operator.itemgetter('node'))
         response['instance_groups'] = []
-        for instance_group in InstanceGroup.objects.all():
+        for instance_group in InstanceGroup.objects.prefetch_related('instances'):
             response['instance_groups'].append(dict(name=instance_group.name,
                                                     capacity=instance_group.capacity,
                                                     instances=[x.hostname for x in instance_group.instances.all()]))