Add podman support

[tfoote]

This is towards #196

As of opening this there are a few known issues.

• --user doesn't work due to "potentially insufficient UIDs or GIDs available in user namespace" when pulling containers/podman#12715 It appears to bottom out in homed does not map subids, causing files owned by the subids to become "nobody" systemd/systemd#21952 then is fixed in systemd/systemd@1af53c0 but that's not available on my system yet.

• It also is still using the docker-deamon storage for building and each podman run command is pulling it across to podman storage before executing which takes a little bit of time for larger images.

• There's no unit testing yet

• Consider a separate command line command instead of using the flag to switch the cli. ruman or something else shortening run podman maybe rodman