Collect details on ARP spoof functional failures

There seems to be some race condition or corner case in the
ARP spoofing functional tests that cause them to randomly
fail in the gate but it's difficult to reproduce them
locally. This patch adds a bunch of details on failures so
we can maybe get some hints about the unexpected state of
the bridge or interfaces that is causing the failure.

Partial-Bug: #1550623
Change-Id: I15b7ab3ce2a95d2b432239d535e3700f28ad21de

neutron/tests/functional/agent/test_ovs_flows.py

@@ -17,7 +17,9 @@ import eventlet
 import fixtures
 import mock
 from oslo_config import cfg
+from oslo_serialization import jsonutils
 from oslo_utils import importutils
+from testtools.content import text_content
 
 from neutron.agent.linux import ip_lib
 from neutron.cmd.sanity import checks
@@ -117,6 +119,7 @@ class _ARPSpoofTestCase(object):
         # NOTE(kevinbenton): it would be way cooler to use scapy for
         # these but scapy requires the python process to be running as
         # root to bind to the ports.
+        self.addOnException(self.collect_flows_and_ports)
         super(_ARPSpoofTestCase, self).setUp()
         self.skip_without_arp_support()
         self.src_addr = '192.168.0.1'
@@ -132,6 +135,21 @@ class _ARPSpoofTestCase(object):
         # wait to add IPs until after anti-spoof rules to ensure ARP doesn't
         # happen before
 
+    def collect_flows_and_ports(self, exc_info):
+        nicevif = lambda x: ['%s=%s' % (k, getattr(x, k))
+                             for k in ['ofport', 'port_name', 'switch',
+                                       'vif_id', 'vif_mac']]
+        nicedev = lambda x: ['%s=%s' % (k, getattr(x, k))
+                             for k in ['name', 'namespace']] + x.addr.list()
+        details = {'flows': self.br.dump_all_flows(),
+                   'vifs': map(nicevif, self.br.get_vif_ports()),
+                   'src_ip': self.src_addr,
+                   'dest_ip': self.dst_addr,
+                   'sourt_port': nicedev(self.src_p),
+                   'dest_port': nicedev(self.dst_p)}
+        self.addDetail('arp-test-state',
+                       text_content(jsonutils.dumps(details, indent=5)))
+
     @common_base.no_skip_on_missing_deps
     def skip_without_arp_support(self):
         if not checks.arp_header_match_supported():