Cleanup in cmdlib for standalone function calls

This patch is a cleanup of the standalone functions in cmdlib. Many of
them too as argument a ConfigWriter instance, but some also took other
parameters from the lu (e.g. proc), and in the future, if we want to
also pass the RpcRunner, we would have to add yet another parameter.

One option is to make all these methods of top-level LogicalUnit class.
I took another approach, and made (almost) all these functions take as
first parameter the lu instance. It's like methods, just not declared
under LogicalUnit.

Reviewed-by: imsnah