docker2podman: pull images from docker daemon

docker2podman: pull images from docker daemon

The docker2podman playbook only installs the podman package and updates
the systemd units with the right container_binary value.

We never pull the container image so if one service is restarted then
the container image will be pulled first before the service can start
which could cause longer downstream.

To avoid to download the container image from internet again we can just
pull it from the local docker daemon.

The container_{binding,package,service}_name variables are removed
because they are only used in the ceph-container-engine role which
isn't call in this playbook.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>