Allow vhost to be maybe opts['rhost']

This enables passing rhost and rport directly to send_request_cgi
without having to monkey with the datastore.

See #8498

lib/msf/core/exploit/http/client.rb

@@ -164,7 +164,7 @@ module Exploit::Remote::HttpClient
 
     # Configure the HTTP client with the supplied parameter
     nclient.set_config(
-      'vhost' => opts['vhost'] || self.vhost(),
+      'vhost' => opts['vhost'] || opts['rhost'] || self.vhost(),
       'agent' => datastore['UserAgent'],
       'uri_encode_mode'        => datastore['HTTP::uri_encode_mode'],
       'uri_full_url'           => datastore['HTTP::uri_full_url'],