Use peer when writing scanner modules

This fixes the module seen in PR rapid7#3684 to use the peer method at the beginning of print_* messages, rather than the vhost method at the end. Doing this tends to make reading the output much easier since it's more consistent.

Incidentally, this module has an msftidy complaint:

````
--- Checking new and changed module syntax with tools/msftidy.rb ---
modules/auxiliary/scanner/http/ipboard_login.rb - [INFO] Please use vars_get in send_request_cgi: send_request_cgi({ 'uri' => normalize_uri(target_uri.path, "index.php?app=core&module=global&section=login&do=process"
````

This should be fixed as well, or explained why it's not being honored.

/cc @OJ @ChrisTruncer