MINOR: smtpchk: Update expect rule to fully match replies to EHLO commands

MINOR: smtpchk: Update expect rule to fully match replies to EHLO commands

The response to EHLO command is a multiline reply. However the corresponding
expect rule only match on the first line. For now, it is not an issue. But
to be able to send the QUIT command and gracefully close the connection, we
must be sure to consume the full EHLO reply first.

To do so, the regex has been updated to match all 2xx lines at a time.