MINOR: acme: display the complete challenge_ready command in the logs

MINOR: acme: display the complete challenge_ready command in the logs

When using a wildcard DNS domain in the ACME configuration, for example
*.example.com, one might think that it needs to use the challenge_ready
command with this domain. But that's not the case, the challenge_ready
command takes the domain asked by the ACME server, which is stripped of
the wildcard.

In order to be clearer, the log message shows exactly the command the
user should sent, which is clearer.