automation: implement (rootless) podman support in containerize

automation: implement (rootless) podman support in containerize

Right now only docker is supported, when using the containerize script
for building inside containers. Enable podman as well.

Note that podman can be use in rootless mode too, but for that to work
the files /etc/subuid and /etc/subgid must be properly configured.

For instance:

dario@localhost> cat /etc/subuid
dario:100000:65536

dario@localhost:> cat /etc/subgid
dario:100000:65536

Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
Acked-by: Wei Liu <wl@xen.org>
Release-acked-by: Paul Durrant <paul@xen.org>