Cannot generate time series files for all variables

[golaz]

Trying to generate time series files for all variables in a set of input files. With ncclimo, this is accomplished by simply omitting the -v command line option.

Unfortunately, this is not possible in zppy because zppy will always add that option and automatically populate it with an atmosphere default list.

[forsyth2]

@golaz It looks like climo already had the ability to generate all variables, by specifying "" for vars. I do the same for ts in #453.