[tripleo] undercloud / standalone have switched to podman by default

For your information, default deployment of Undercloud and Standalone are now using Podman instead of Docker by default. The switch doesn't affect the Overcloud yet but we also aim to change the default before the end of Stein release. If you still want to use docker: * For Undercloud: undercloud.conf : container_cli = docker * For Standalone: in your environment: ContainerCli: docker Please let us know any problem regarding that change. -- Emilien Macchi