Require cloud on inventory source for notification

Inventory Sources must now be a cloud type in order to associate a
notification template with it.

awx/main/tests/functional/test_inventory.py

@@ -0,0 +1,19 @@
+import pytest
+
+from django.core.urlresolvers import reverse
+
+@pytest.mark.django_db
+def test_inventory_source_notification_on_cloud_only(get, post, group, user, notification_template):
+    u = user('admin', True)
+    g_cloud = group('cloud')
+    g_not = group('not_cloud')
+    cloud_is = g_cloud.inventory_source
+    not_is = g_not.inventory_source
+    cloud_is.source = 'ec2'
+    cloud_is.save()
+    url = reverse('api:inventory_source_notification_templates_any_list', args=(cloud_is.id,))
+    response = post(url, dict(id=notification_template.id), u)
+    assert response.status_code == 204
+    url = reverse('api:inventory_source_notification_templates_success_list', args=(not_is.id,))
+    response = post(url, dict(id=notification_template.id), u)
+    assert response.status_code == 400