Use global capacity algorithm in serializer

The task manager was doing work to compute currently consumed
capacity, this is moved into the manager and applied in the
same form to the instance group list.

awx/main/models/ha.py

@@ -11,7 +11,7 @@ from django.utils.timezone import now, timedelta
 from solo.models import SingletonModel
 
 from awx.api.versioning import reverse
-from awx.main.managers import InstanceManager
+from awx.main.managers import InstanceManager, InstanceGroupManager
 from awx.main.models.inventory import InventoryUpdate
 from awx.main.models.jobs import Job
 from awx.main.models.projects import ProjectUpdate
@@ -66,6 +66,8 @@ class Instance(models.Model):
 
 class InstanceGroup(models.Model):
     """A model representing a Queue/Group of AWX Instances."""
+    objects = InstanceGroupManager()
+
     name = models.CharField(max_length=250, unique=True)
     created = models.DateTimeField(auto_now_add=True)
     modified = models.DateTimeField(auto_now=True)
@@ -89,12 +91,7 @@ class InstanceGroup(models.Model):
 
     @property
     def capacity(self):
-        return sum([x[0] for x in self.instances.values_list('capacity')])
-
-    @property
-    def consumed_capacity(self):
-        return sum(x.task_impact for x in UnifiedJob.objects.filter(instance_group=self,
-                                                                    status__in=('running', 'waiting')))
+        return sum([inst.capacity for inst in self.instances.all()])
 
     class Meta:
         app_label = 'main'