Land rapid7#6599, fix silent failures in aux HttpServers

Author: egypt

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

@@ -73,7 +73,7 @@ def cli=(cli)
   end
 
   def print_prefix
-    if cli && !aggressive?
+    if cli && (respond_to?(:aggressive) && !aggressive?)
       super + "#{cli.peerhost.ljust(16)} #{self.shortname} - "
     else
       super