Implemented, by moving upgrade functionality from install_upgrade.escript
to nodetool, which already supports both short and long names.
Make install_upgrade.escript as wrapper for nodetool for backward compatibility.
* Typos and other minor bug fixes
* Add "attach" command (via -remsh)
* Add "upgrade" command to install a hot upgrade package
* Add "upgrade" subcommand to UNIX runner script as well