more gracefully account for undefined stdout

see: https://github.com/ansible/tower/issues/1215
related: https://github.com/ansible/tower/pull/1192#issuecomment-377982131

awx/main/tasks.py

@@ -885,6 +885,7 @@ class BaseTask(LogErrorsTask):
         output_replacements = []
         extra_update_fields = {}
         event_ct = 0
+        stdout_handle = None
         try:
             kwargs['isolated'] = isolated_host is not None
             self.pre_run_hook(instance, **kwargs)

awx/main/tests/unit/test_tasks.py

@@ -13,6 +13,7 @@ import fcntl
 import mock
 import pytest
 import yaml
+
 from django.conf import settings
 
 
@@ -295,6 +296,15 @@ class TestJobExecution:
 
 class TestGenericRun(TestJobExecution):
 
+    def test_generic_failure(self):
+        self.task.build_private_data_files = mock.Mock(side_effect=IOError())
+        with pytest.raises(Exception):
+            self.task.run(self.pk)
+        update_model_call = self.task.update_model.call_args[1]
+        assert 'IOError' in update_model_call['result_traceback']
+        assert update_model_call['status'] == 'error'
+        assert update_model_call['emitted_events'] == 0
+
     def test_cancel_flag(self):
         self.instance.cancel_flag = True
         with pytest.raises(Exception):