Implementing models for instance groups, updating task manager

* New InstanceGroup model and associative relationship with Instances
* Associative instances between Organizations, Inventory, and Job
  Templates and InstanceGroups
* Migrations for adding fields and tables for Instance Groups
* Adding activity stream reference for instance groups
* Task Manager Refactoring:
** Simplifying task manager relationships and move away from the
   interstitial hash tables
** Simplify dependency determination logic
** Reduce task manager runtime complexity by removing the partial
   references and moving the logic into the task manager directly or
   relying on Job model logic for determinism

awx/main/models/ha.py

@@ -4,6 +4,7 @@
 from django.db import models
 from django.db.models.signals import post_save
 from django.dispatch import receiver
+from django.utils.translation import ugettext_lazy as _
 
 from solo.models import SingletonModel
 
@@ -17,9 +18,7 @@ __all__ = ('Instance', 'JobOrigin', 'TowerScheduleState',)
 
 
 class Instance(models.Model):
-    """A model representing an Ansible Tower instance, primary or secondary,
-    running against this database.
-    """
+    """A model representing an Ansible Tower instance running against this database."""
     objects = InstanceManager()
 
     uuid = models.CharField(max_length=40)
@@ -41,6 +40,22 @@ class Instance(models.Model):
         return "tower"
 
 
+class InstanceGroup(models.Model):
+    """A model representing a Queue/Group of Tower Instances."""
+    name = models.CharField(max_length=250, unique=True)
+    created = models.DateTimeField(auto_now_add=True)
+    modified = models.DateTimeField(auto_now=True)
+    instances = models.ManyToManyField(
+        'Instance',
+        related_name='rampart_groups',
+        editable=False,
+        help_text=_('Instances that are members of this InstanceGroup'),
+    )
+
+    class Meta:
+        app_label = 'main'
+
+
 class TowerScheduleState(SingletonModel):
     schedule_last_run = models.DateTimeField(auto_now_add=True)