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
3 files changed