Introduce xml variable controlling reseeding and snow resetting

**Bill Sacks < sacks@ucar.edu > - 2017-03-31 15:00:36 -0600**
**Bugzilla Id:** [2438](http://bugz.cgd.ucar.edu/show_bug.cgi?id=2438)
**Bugzilla CC:** rfisher@ucar.edu,

We'd like to have a single xml variable (proposed name RESET_SNOW_N_SEEDS_CLM_FOR_COUPLED_RUN) that controls both:

(1) whether to do reseeding

(2) whether to reset snow (reset_snow - new namelist variabl)

since those are typically done at the same time.