Change nodetool to permit zero parameter rpc calls

Change nodetool so that functions of zero arity may be called using
the supplied rpc facility. This is done by making a distinction
between the case when rpc parameters are present and when they are
not.

Previously calling zero arity functions has not been possible because
even submitting no rpc parameters is treated the same as submitting
the request with a single parameter of an empty list.  Nodetool
encapsulates any parameters as a list and the result of attempting to
call a function that takes no parameters was the rpc function calling
the supplied function with a single parameter of an empty list.

This change does not preclude calling functions with a single
parameter of an empty list. It just now makes that decision explicit
on the part of the caller.
Revert "Merge branch 'feature/nodetool-zero-arg-rpc' into develop"

This reverts commit 93db72ef65d714e5e8d849fff558be3940992f2a, reversing
changes made to a56fe9b021e3543a24fdfc98f1c16704b41e62c6.
Fix typo in README for package_patch_dir
Add example app to help with documentation
add support for custom exit codes to nodetool rpc & friends