Comment 1 for bug 1814275

The main issue looks like we're mapping /home/stack/undercloud.conf to /var/lib/mistral/undercloud.conf as read-only: https://github.com/openstack/tripleo-heat-templates/blob/master/deployment/mistral/mistral-executor-container-puppet.yaml#L183

But when running the mistral command, we set the permission field to change the ownership for the whole /var/lib/mistral directory (in a recursive manner) and as undercloud.conf is a read-only file we fail. The easies solution is to just map the undercloud.conf as rw.