tempurl: Fix PUT upload to temp url on py3

Without this change, the self._response_headers gets a dict_items() type
on PUT. But the rest of the code assumes that it is a list.

Bug manifestation:

    File "swift/common/middleware/catch_errors.py", line 120,
        in handle_request
      self._response_headers.append(('X-Trans-Id', trans_id))
  AttributeError: 'dict_items' object has no attribute 'append'

Closes-Bug: #1929083
Change-Id: I5c398b6008716b64c668737e4201ba3b6ab3320b

swift/common/middleware/tempurl.py

@@ -839,7 +839,7 @@ class TempURL(object):
                     if h.startswith(p):
                         del headers[h]
                         break
-        return headers.items()
+        return list(headers.items())
 
 
 def filter_factory(global_conf, **local_conf):

test/unit/common/middleware/test_tempurl.py

@@ -476,6 +476,42 @@ class TestTempURL(unittest.TestCase):
         self.assertEqual(req.environ['swift.authorize_override'], True)
         self.assertEqual(req.environ['REMOTE_USER'], '.wsgi.tempurl')
 
+    def test_put_response_headers_in_list(self):
+        class Validator(object):
+            def __init__(self, app):
+                self.app = app
+                self.status = None
+                self.headers = None
+                self.exc_info = None
+
+            def start_response(self, status, headers, exc_info=None):
+                self.status = status
+                self.headers = headers
+                self.exc_info = exc_info
+
+            def __call__(self, env, start_response):
+                resp_iter = self.app(env, self.start_response)
+                start_response(self.status, self.headers, self.exc_info)
+                return resp_iter
+
+        method = 'PUT'
+        expires = int(time() + 86400)
+        path = '/v1/a/c/o'
+        key = b'abc'
+        hmac_body = ('%s\n%i\n%s' % (method, expires, path)).encode('utf-8')
+        sig = hmac.new(key, hmac_body, hashlib.sha1).hexdigest()
+        req = self._make_request(
+            path, keys=[key],
+            environ={'REQUEST_METHOD': 'PUT',
+                     'QUERY_STRING': 'temp_url_sig=%s&temp_url_expires=%s' % (
+                         sig, expires)})
+        validator = Validator(self.tempurl)
+        resp = req.get_response(validator)
+        self.assertIsInstance(validator.headers, list)
+        self.assertEqual(resp.status_int, 404)
+        self.assertEqual(req.environ['swift.authorize_override'], True)
+        self.assertEqual(req.environ['REMOTE_USER'], '.wsgi.tempurl')
+
     def test_get_not_allowed_by_put(self):
         method = 'PUT'
         expires = int(time() + 86400)