buffer() was removed in Python 3 so use bytes (#1218)

* buffer() was removed in Python 3 so use memoryview

https://docs.python.org/2.7/library/stdtypes.html#memoryview-type

* buffer = bytes on Python 3

* from kombu.five import buffer

* buffer --> buffer_t

* @patch('buffer_t') in test_qpid.py

* @patch('kombu.five.buffer_t')

* Use buffer on legacy Python and bytes on Python

* Update test_qpid.py

kombu/transport/qpid.py

@@ -124,6 +124,10 @@ from kombu.transport import base, virtual
 
 logger = get_logger(__name__)
 
+try:
+    buffer
+except NameError:
+    buffer = bytes
 
 OBJECT_ALREADY_EXISTS_STRING = 'object already exists'