* Consistently use just the hostname as the log message prefix.
  * Delete redundant verbose log message.
  * Log IPv4 and IPv6 separately in case `$ipv4` or `$ipv6` is
    `undef`.
  * Don't log the full line when a known error result is returned.
  * For unknown results, don't wrap the line in parentheses.
  * Use string interpolation for readability.

Before:
  * `$scale` was ignored causing it to set `wtime` to 5s in the
    future, which is too brief.  Fortunately, `min-error-interval`
    applied which prevented overly aggressive retries.
  * The lack of call to `failed` meant that `$result` was not set to
    "FAILED" and thus `mail-failure` recipients were not emailed.

Now `TOOSOON` is treated like any other error and will result in a
retry after `min-error-interval` (default: 5m).

The server returns a full HTML document, not just the result code.
Change equality check to a regex match that is resilient to
server-side changes.