fix: reverse docker socket test

[buchdag]

Fix proposed by @andrei-datcu for #1179

The entrypoint will fail if test -S $socket_file is false but only display a warning if test -r $socket_file is false.

[andrei-datcu]

I don't have the proper historical context of why the -r check was introduced, but for the original problem the check tried to resolve would this change work or would the -S check fail before -r test would get a chance to run? I was thinking the -r check would only be done if the -S failed to try and output a more explicit error message.

[buchdag]

The -r check was added here #1149

So maybe something like this instead ?

if [[ ! -S $socket_file ]]; then
    if [[ ! -r $socket_file ]]; then
        echo "Warning: Docker host socket at $socket_file might not be readable. Please check user permissions" >&2
        echo "If you are in a SELinux environment, try using: '-v /var/run/docker.sock:$socket_file:z'" >&2
    fi
    echo "Error: you need to share your Docker host socket with a volume at $socket_file" >&2
    echo "Typically you should run your container with: '-v /var/run/docker.sock:$socket_file:ro'" >&2
    exit 1
fi

[andrei-datcu]

Yes, that looks better to me.

[buchdag]

Done, pushed as nginxproxy/acme-companion:1182 if you wish to try it before we merge this.

[andrei-datcu]

I've just tested it and it's working nicely. Thank you! :)