Handle KnownHosts

[manuel-rubio]

To be more secure we have to configure the use of known hosts (or at least let to the user handle them) to ensure it's connecting to the correct server. The option for the ssh modules (connect functions) is:

{silently_accept_hosts, CallbackFun} 

We can create a configuration option to by-pass this or do it in the same way we did with the keys.