This allows us to continue execution until a certain proportion of hosts
fail. This can be useful at scale, where failures are common, and
restarting a deployment is time-consuming.

The default max failure percentage is 100, keeping the default
behaviour. A global max failure percentage may be set via
kayobe_max_fail_percentage, and individual playbooks may define a max
failure percentage via <playbook>_max_fail_percentage.

Related Kolla Ansible patch:
https://review.opendev.org/c/openstack/kolla-ansible/+/805598

Change-Id: Ib81c72b63be5765cca664c38141ffc769640cf07