Extend network debug infos on network failures

After the https://review.openstack.org/#/c/76640/ is merge tempest will
be allowed to dump the ovs db.

The ovs db dump can help in identifying trunk/access port miss configuration
issues.

Change-Id: Ia751dc5046ce07369b9044eda3b20c63d38bac99
diff --git a/tempest/common/debug.py b/tempest/common/debug.py
index 8325d4d..6a496c2 100644
--- a/tempest/common/debug.py
+++ b/tempest/common/debug.py
@@ -38,3 +38,15 @@
         for table in ['filter', 'nat', 'mangle']:
             LOG.info('ns(%s) table(%s):\n%s', ns, table,
                      commands.iptables_ns(ns, table))
+
+
+def log_ovs_db():
+    if not CONF.debug.enable or not CONF.service_available.neutron:
+        return
+    db_dump = commands.ovs_db_dump()
+    LOG.info("OVS DB:\n" + db_dump)
+
+
+def log_net_debug():
+    log_ip_ns()
+    log_ovs_db()