Disable siblings for the cindelib functional tests

Follow the same pattern of the other jobs which deploy devstack
but runs also functional tests (see devtack-tox-functional
and devstack-tox-functional-consumer).

Without this, the older branches where cinderlib functional tests
use Python 2 (stein, and soon train when that is branched) fails
because they try to install packages part of which are Python 3
only.

Change-Id: Ibd2862f30d4c451118fb96d1f56a09fd66b2d75a
diff --git a/playbooks/tempest-and-cinderlib-run.yaml b/playbooks/tempest-and-cinderlib-run.yaml
index ff99d08..8e26913 100644
--- a/playbooks/tempest-and-cinderlib-run.yaml
+++ b/playbooks/tempest-and-cinderlib-run.yaml
@@ -25,6 +25,7 @@
       devstack_data_subdir_changed: cinder
       devstack_data_subdir_owner: zuul
     - role: run-cinderlib-tests
+      tox_install_siblings: false
       cinderlib_base_dir: "{{ ansible_user_dir }}/{{ zuul.projects['opendev.org/openstack/cinderlib'].src_dir }}"
   post_tasks:
     - name: Fail if the first tempest run did not work