Implement request_pty

[Deleted user]

http://net-ssh.rubyforge.org/ssh/v2/api/index.html

Otherwise non-root users are not able to run commands with sudo on systems with Defaults requiretty in /etc/sudoers (e.g. Rackspace nodes)

[Deleted user]

Current problem: ch.request_pty works for commands but breaks file uploads.