When acme-client is run with -v, show the account URI from the Location

When acme-client is run with -v, show the account URI from the Location
header sent by the server in response to the newAccount API call (used for
every cert request). This is useful if you want to set a CAA DNS record
restricting issuance to a specific user account, rather than just "all of
$whichever_acme_CA".  ok florian