Fix dhcpv6-stateful tempest test to validate only valid use-cases

[Sridhar Gaddam]

According to IPv6 Radvd implementation[1], when ipv6_ra_mode is not set
and ipv6_address_mode is set to dhcpv6-stateful, Neutron would be
using an external router for Router Advertisements. Such subnets are
not supposed to be associated with Neutron Router as they are meant to
be used with external router.

A recent commit I0a063e543e320ea625a5411547bce7fa2ad66b7d is causing
failure of the Neutron patch[2] in gate. The api, test_dhcp_stateful_router, has
to be suitably modified to remove the invalid use-case.

[1] - http://specs.openstack.org/openstack/neutron-specs/specs/juno/ipv6-radvd-ra.html#rest-api-impact
[2] - https://review.openstack.org/#/c/136733

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/143014

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/143014
Committed: https://git.openstack.org/cgit/openstack/tempest/commit/?id=ba3aee5a9c9df7c2b471da4e6d1d48a60a97ab9d
Submitter: Jenkins
Branch: master

commit ba3aee5a9c9df7c2b471da4e6d1d48a60a97ab9d
Author: sridhargaddam <email address hidden>
Date: Fri Dec 19 08:26:45 2014 +0000

    Fix dhcpv6-stateful tempest test to validate only valid use-case

    According to IPv6 Radvd implementation[1], when ipv6_ra_mode is not set
    and ipv6_address_mode is set to dhcpv6-stateful, Neutron would be using
    an external router for Router Advertisements. Such subnets are not
    supposed to be associated with Neutron Router as they are meant to be
    used with external router.

    A recent commit I0a063e543e320ea625a5411547bce7fa2ad66b7d is causing
    failure of the Neutron patch[2] in gate. This patch modifies the tempest
    code to remove this invalid use-case and validate only the valid
    use-cases.

    [1] - Neutron ipv6-radvd-ra blueprint
    [2] - https://review.openstack.org/#/c/136733/6

    Closes-Bug: #1404139
    Change-Id: Ib17d1e92d5491aa49a58717ba158f339a1c5f366