dbuild: Fix podman invocation (#5481)
dbuild: Fix podman invocation (#5481)

The is_podman check was depending on `docker -v` printing "podman" in
the output, but that doesn't actually work, since podman prints $0.
Use `docker --help` instead, which will output "podman".

Also return podman's return status, which was previously being
dropped.

Signed-off-by: Dejan Mircevski <1e9694aae17a51d4875d9bf4a0d0e20ef37c1b85@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla