cleanup for sami_ftpd_list

Hi @dougsko,

This pull request references https://github.com/rapid7/metasploit-framework/pull/1609 . The submission is still unstable because of badchars and/or sometimes the decoder crashing.

I've tried to make it more stable:

* Finishing badchars analysis
* Disabling nops before payload (they aren't needed in fact)
* Stackpivoting before the encoder

Also I've noticed login isn't needed to exploit, so I've switched from connect_login to connect. Finally a little of module cleanup.

Feel free to review the changes and ask anything. Once you're comfortable with changes, feel free to merge it into your repo, so https://github.com/rapid7/metasploit-framework/pull/1609 will be updated automatically and we'll be mainly ready to merge :)

Thanks!