Support AWX_TASK_ENV injection in task and notification invocations.

This change _only_ injects `AWS_TASK_ENV` into `os.environ`; it's up to
underlying libraries to be good citizens and actually respect things
like `HTTPS_PROXY`.

see: #3508

awx/main/tests/functional/test_notifications.py

@@ -1,6 +1,10 @@
 import mock
 import pytest
 
+from requests.adapters import HTTPAdapter
+from requests.utils import select_proxy
+from requests.exceptions import ConnectionError
+
 from awx.api.versioning import reverse
 from awx.main.models.notifications import NotificationTemplate, Notification
 from awx.main.models.inventory import Inventory, InventorySource
@@ -129,3 +133,26 @@ def test_disallow_delete_when_notifications_pending(delete, user, notification_t
     response = delete(url, user=u)
     assert response.status_code == 405
 
+
+@pytest.mark.django_db
+def test_custom_environment_injection(post, user, organization):
+    u = user('admin-poster', True)
+    url = reverse('api:notification_template_list')
+    response = post(url,
+                    dict(name="test-webhook",
+                         description="test webhook",
+                         organization=organization.id,
+                         notification_type="webhook",
+                         notification_configuration=dict(url="https://example.org",
+                                                         headers={"Test": "Header"})),
+                    u)
+    assert response.status_code == 201
+    template = NotificationTemplate.objects.get(pk=response.data['id'])
+    with pytest.raises(ConnectionError), \
+            mock.patch('django.conf.settings.AWX_TASK_ENV', {'HTTPS_PROXY': '192.168.50.100:1234'}), \
+            mock.patch.object(HTTPAdapter, 'send') as fake_send:
+        def _send_side_effect(request, **kw):
+            assert select_proxy(request.url, kw['proxies']) == '192.168.50.100:1234'
+            raise ConnectionError()
+        fake_send.side_effect = _send_side_effect
+        template.send('subject', 'message')