Experimental Podman support does not work by default for docker_environments

[sureshjoshi]

I ran into an issue where I needed to manually add DOCKER_HOST to pants.toml and pass in the location to my Podman socket, in order to perform a docker pull.

I haven’t fully dug into this, but this feels like it’s coming from Bollard (and likely docker_environment). Without the DOCKER_HOST, I get a /var/run/docker.sock error, which comes from Bollard.

As far as I can tell, most docker/podman interactions are done via CLI - otherwise.