refactor(autotest): restructure netcdf tests to remove duplicate code (MODFLOW-ORG#1906)

* refactor netcdf tests

* improvements based on suggestion

* add missing netcdf marks

* restore test_gwt_dsp01.py

---------

Co-authored-by: mjreno <mjreno@IGSAAA071L01144.gs.doi.net>

Author: mjreno