namelist input. Also, choose name of primary NetCDF variable in
namelist and read only this variable, not its coordinates. This makes
it easier to use an arbitrary NetCDF file.

In program test_set_outermost_contour, it is hard to remember the
order of positional arguments so we rather use fixed input file names
and no arguments.

In JSON input file for tests, it is simpler to use the "input" key
than creating a one-line input file, in some cases.