Move verify-ipv6-only-deployments

from Tempest to DevStack as it tests DevStack side of things and
is useful for projects not using Tempest.

Verbatim copy except for the devstack- prefix and the /devstack/
path.

Change-Id: Ie166730843f874b9c99e37244e460d7ad33b7eeb
diff --git a/roles/devstack-ipv6-only-deployments-verification/tasks/main.yaml b/roles/devstack-ipv6-only-deployments-verification/tasks/main.yaml
new file mode 100644
index 0000000..59d3b79
--- /dev/null
+++ b/roles/devstack-ipv6-only-deployments-verification/tasks/main.yaml
@@ -0,0 +1,4 @@
+- name: Verify the ipv6-only deployments
+  become: true
+  become_user: stack
+  shell: "{{ devstack_base_dir }}/devstack/tools/verify-ipv6-only-deployments.sh"