* Support Podman for mocking Lambda
Podman supports all Docker APIs used in moto since version 3.0. Note
that Podman requires pulling the image before creating a container
using a fully-qualified image name (e.g., "docker.io/library/busybox"
instead of "busybox").
Test plan:
$ podman system service -t 0
$ DOCKER_HOST="unix://$XDG_RUNTIME_DIR/podman/podman.sock" pytest
Fixes https://github.com/spulec/moto/issues/3276
* Run black
* Python 2 compatibility
* Address review comments and improve parse_image_ref
