Fix testing IPv6 VIP network connectivity

The IPv6 VIP subnet used in the tests is created using devstack's
default IPv6 subnetpool.
Devstack ensures that any CIDR from this subnetpool is routable from the
devstack node if the subnet is plugged into devstack's router1.

Change-Id: Iaf3113087a344787add3405208fb229838a56d0b
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index f44bf96..7af7a1f 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -179,6 +179,13 @@
     cfg.StrOpt('member_2_ipv6_subnet_cidr',
                default='fd77:1457:4cf0:26a8::/64',
                help='CIDR format subnet to use for the member 1 ipv6 subnet.'),
+    cfg.StrOpt('default_router',
+               default='router1',
+               help='The default router connected to the public network.'),
+    cfg.StrOpt('default_ipv6_subnetpool',
+               default='shared-default-subnetpool-v6',
+               help='The default IPv6 subnetpool to use when creating the '
+                    'IPv6 VIP subnet.'),
     # Amphora specific options
     cfg.StrOpt('amphora_ssh_user',
                default='ubuntu',