log when the default podman system connection is the rootless one

[vrothberg]

I just ran into the situation where my default connection (see podman system connect ls) was set to the rootless user. Since podman-bootc uses the root user of the Podman Machine, we can run into a confusing situation where podman-bootc can (not) see images but podman can (not).

Throwing a log/warning in that case can reduce the confusion.

[vrothberg]

Cc: @cgwalters @germag

[evan-goode]

I had this problem too:

evan@barb ~ $ podman run --rm -it localhost/bootc-test /bin/true
evan@barb ~ $ podman-bootc run localhost/bootc-test                     
Trying to pull localhost/bootc-test:latest...
Error: unable to install bootc image: failed to pull image: initializing source docker://localhost/bootc-test:latest: pinging container registry localhost: Get "https://localhost/v2/": dial tcp [::1]:443: connect: connection refused

Here is my podman system connection ls:

Name                         URI                                                          Identity                                                   Default     ReadWrite
podman-machine-default       ssh://core@127.0.0.1:44369/run/user/1000/podman/podman.sock  /home/evan/.local/share/containers/podman/machine/machine  false       true
podman-machine-default-root  ssh://root@127.0.0.1:44369/run/podman/podman.sock            /home/evan/.local/share/containers/podman/machine/machine  true        true

Huh, podman-machine-default-root is listed as the default connection, but podman images and podman -c podman-machine-default-root images have totally different output. I might have some manual reading in my future.

As a workaround, I passed -c podman-machine-default-root when building the container:

podman -c podman-machine-default-root build -f Containerfile -t localhost/bootc-test

Possibly related: #9