Address the SFTP logon issues (timeout waiting for keypress, node status, etc)

For SFTP sessions, there's no shell/terminal, so no need to run command
shells (with their input timeouts, etc.). Reflect the node connection as
"via sftp" in the node status. Handle node interruption signal. Probably more
to do here with node status/actions (e.g. it'd be nice to set the action to
"uploading or "downloading" when appropriate).