I'm seeing something similar on Tripleo/Fedora

 ERROR nova.api.openstack [req-b249d867-efa9-4b69-bb00-bcd188d35d95 f6aafe318df1469498437c69e9f20206 677e5e66567a4d1ebe0b1946452a03ef] Ca
 TRACE nova.api.openstack Traceback (most recent call last):                     
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/__init__.py", line 120, in __call_
 TRACE nova.api.openstack     return req.get_response(self.application)          
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/request.py", line 1296, in send
 TRACE nova.api.openstack     application, catch_exc_info=False)                 
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/request.py", line 1260, in call_application
 TRACE nova.api.openstack     app_iter = application(self.environ, start_response)
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/dec.py", line 144, in __call__
 TRACE nova.api.openstack     return resp(environ, start_response)               
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/keystoneclient/middleware/auth_token.py", line 571, in __call__
 TRACE nova.api.openstack     return self.app(env, start_response)               
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/dec.py", line 144, in __call__
 TRACE nova.api.openstack     return resp(environ, start_response)               
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/dec.py", line 144, in __call__
 TRACE nova.api.openstack     return resp(environ, start_response)               
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/routes/middleware.py", line 131, in __call__
 TRACE nova.api.openstack     response = self.app(environ, start_response)       
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/dec.py", line 144, in __call__
 TRACE nova.api.openstack     return resp(environ, start_response)               
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/dec.py", line 130, in __call__
 TRACE nova.api.openstack     resp = self.call_func(req, *args, **self.kwargs)   
 TRACE nova.api.openstack   File "/usr/lib/python2.7/site-packages/webob/dec.py", line 195, in call_func
 TRACE nova.api.openstack     return self.func(req, *args, **kwargs)             
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/wsgi.py", line 940, in __call__
 TRACE nova.api.openstack     content_type, body, accept)                        
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/wsgi.py", line 1025, in _process_s
 TRACE nova.api.openstack     request, action_args)                              
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/wsgi.py", line 913, in post_proces
 TRACE nova.api.openstack     **action_args)                                     
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/compute/contrib/security_groups.py
 TRACE nova.api.openstack     return self._show(req, resp_obj)                   
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/compute/contrib/security_groups.py
 TRACE nova.api.openstack     self._extend_servers(req, [resp_obj.obj['server']])
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/api/openstack/compute/contrib/security_groups.py
 TRACE nova.api.openstack     servers[0]['id']))                                 
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/nova/network/security_group/neutron_driver.py", line 
 TRACE nova.api.openstack     ports = neutron.list_ports(**params)               
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/neutronclient/v2_0/client.py", line 108, in with_para
 TRACE nova.api.openstack     ret = self.function(instance, *args, **kwargs)     
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/neutronclient/v2_0/client.py", line 298, in list_port
 TRACE nova.api.openstack     **_params)                                         
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/neutronclient/v2_0/client.py", line 1197, in list
 TRACE nova.api.openstack     for r in self._pagination(collection, path, **params):
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/neutronclient/v2_0/client.py", line 1210, in _paginat
 TRACE nova.api.openstack     res = self.get(path, params=params)                
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/neutronclient/v2_0/client.py", line 1183, in get
 TRACE nova.api.openstack     headers=headers, params=params)                    
 TRACE nova.api.openstack   File "/opt/stack/venvs/nova/lib/python2.7/site-packages/neutronclient/v2_0/client.py", line 1175, in retry_re
 TRACE nova.api.openstack     raise exceptions.ConnectionFailed(reason=_("Maximum attempts reached"))   
 TRACE nova.api.openstack ConnectionFailed: Connection to neutron failed: Maximum attempts reached
 TRACE nova.api.openstack                                                        

I looks like http requests/responses over persistent tcp connections to neutron are happening out of order
See the first two http requests attached (from same TCP connection)