Ansible>=2.3.0 will output warnings if `when` statements contain jinja2 templating delimiters such as curly braces (the playbooks are executing fine, despite the warnings). Exemples: https://ci.centos.org/artifacts/rdo/jenkins-tripleo-quickstart-extras-gate-newton-delorean-full-minimal-2319/undercloud/home/stack/run_preintro_validations_negative_tests.log.gz
A patch has been pushed to the upstream openstack gerrit by Florian. Just created the bug here for tracking potential backport.
Added a backport patch: https://review.openstack.org/510042
Verified in: openstack-tripleo-validations-8.4.0-2.el7ost.noarch
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHEA-2018:2086