Fix intermittent v2 shell unit test failures

The do_image_download code has a check to make sure that there's
a place to put the data (either filename or stdout redirect) before
initiating the download.  The location of this check was moved by
change I841bebeda38814235079429eca0b1e5fd2f04dae to happen at the
beginning of the function.  The two intermittently failing tests
do not explicitly address the check condition, and as a result the
tests do exit early, but before they can check what they're supposed
to be testing.

Closes-bug: #1759951

Change-Id: I3c85bb358f669504b364d55618c21382b7a2a66b

glanceclient/tests/unit/v2/test_shell_v2.py

@@ -758,10 +758,13 @@ class ShellV2Test(testtools.TestCase):
             self.assert_exits_with_msg(func=test_shell.do_image_delete,
                                        func_args=args)
 
+    @mock.patch('sys.stdout', autospec=True)
     @mock.patch.object(utils, 'print_err')
-    def test_do_image_download_with_forbidden_id(self, mocked_print_err):
+    def test_do_image_download_with_forbidden_id(self, mocked_print_err,
+                                                 mocked_stdout):
         args = self._make_args({'id': 'IMG-01', 'file': None,
                                 'progress': False})
+        mocked_stdout.isatty = lambda: False
         with mock.patch.object(self.gc.images, 'data') as mocked_data:
             mocked_data.side_effect = exc.HTTPForbidden
             try:
@@ -773,10 +776,12 @@ class ShellV2Test(testtools.TestCase):
             self.assertEqual(1, mocked_data.call_count)
             self.assertEqual(1, mocked_print_err.call_count)
 
+    @mock.patch('sys.stdout', autospec=True)
     @mock.patch.object(utils, 'print_err')
-    def test_do_image_download_with_500(self, mocked_print_err):
+    def test_do_image_download_with_500(self, mocked_print_err, mocked_stdout):
         args = self._make_args({'id': 'IMG-01', 'file': None,
                                 'progress': False})
+        mocked_stdout.isatty = lambda: False
         with mock.patch.object(self.gc.images, 'data') as mocked_data:
             mocked_data.side_effect = exc.HTTPInternalServerError
             try: