Open-code eventlet.listen()

Recently out gate started blowing up intermittently with a strange
case of ports mixed up. Sometimes a functional tests tries to
authorize on a port that's clearly an object server port, and
the like. As it turns out, eventlet developers added an unavoidable
SO_REUSEPORT into listen(), which makes listen(("localhost",0)
to reuse ports.

There's an issue about it:
 https://github.com/eventlet/eventlet/issues/411

This patch is working around the problem while eventlet people
consider the issue.

Change-Id: I67522909f96495a6a30e1acdb79835dce2189549

test/unit/helpers.py

@@ -27,7 +27,7 @@ from tempfile import mkdtemp
 import time
 
 
-from eventlet import listen, spawn, wsgi
+from eventlet import spawn, wsgi
 import mock
 from shutil import rmtree
 import six.moves.cPickle as pickle
@@ -45,6 +45,7 @@ from swift.obj import server as object_server
 from swift.proxy import server as proxy_server
 import swift.proxy.controllers.obj
 
+from test import listen_zero
 from test.unit import write_fake_ring, DEFAULT_TEST_EC_TYPE, debug_logger, \
     connect_tcp, readuntil2crlfs
 
@@ -93,17 +94,17 @@ def setup_servers(the_object_server=object_server, extra_conf=None):
             'allow_versions': 't'}
     if extra_conf:
         conf.update(extra_conf)
-    prolis = listen(('localhost', 0))
-    acc1lis = listen(('localhost', 0))
-    acc2lis = listen(('localhost', 0))
-    con1lis = listen(('localhost', 0))
-    con2lis = listen(('localhost', 0))
-    obj1lis = listen(('localhost', 0))
-    obj2lis = listen(('localhost', 0))
-    obj3lis = listen(('localhost', 0))
-    obj4lis = listen(('localhost', 0))
-    obj5lis = listen(('localhost', 0))
-    obj6lis = listen(('localhost', 0))
+    prolis = listen_zero()
+    acc1lis = listen_zero()
+    acc2lis = listen_zero()
+    con1lis = listen_zero()
+    con2lis = listen_zero()
+    obj1lis = listen_zero()
+    obj2lis = listen_zero()
+    obj3lis = listen_zero()
+    obj4lis = listen_zero()
+    obj5lis = listen_zero()
+    obj6lis = listen_zero()
     objsocks = [obj1lis, obj2lis, obj3lis, obj4lis, obj5lis, obj6lis]
     context["test_sockets"] = \
         (prolis, acc1lis, acc2lis, con1lis, con2lis, obj1lis, obj2lis, obj3lis,