Missing config false flag

the sshexec exploit was missing the flag
that tells net:ssh to not use the user's
local config . This can cuase ugly problem

MSP-9262

modules/exploits/multi/ssh/sshexec.rb

@@ -98,6 +98,7 @@ class Metasploit3 < Msf::Exploit::Remote
       :msfmodule     => self,
       :port          => port,
       :disable_agent => true,
+      :config        => false,
       :password      => pass
     }