Fix WPS regtest.

[AMLattanzi]

This PR corrects the WPS regtest failure.

We have defined the following:
#define NDRY 4
#define NSCALARS 1
#define NMOIST_max 6
#define NBCVAR_max (NDRY + 1 + NMOIST_max)

But did not propagate that change to the BC vars (BCVars only goes up to RhoQ2_bc_comp). Therefore, we had uninitialized data when constructing the BC types. Recent changes to Dirichlet walls check if the bc value is not equal to the initial bc value to identify a Dirichlet condition with NoSlip or Slip walls. The uninitialized data caused this block of code to be true when it shouldn't have been. The correction in this PR is to simply initialize all of the BC components.