Correct diffusion coefficients for tke in LES (#2034)

TYPE: bug-fix

KEYWORDS: Diffusion of tke

SOURCE: internal (issue raised by Branko Kosovic)

DESCRIPTION OF CHANGES:
Problem:
Reported in #2026 For km_opt=2, tke diffusion should be twice momentum diffusion, but was twice heat diffusion (three times larger). For km_opt=5 it was 3 times momentum diffusion instead of twice.

Solution:
xkmv and xkmh passed into diffusion routines for tke calls instead of xkhv and xkhh.

ISSUE: For use when this PR closes an issue.
Fixes #2026 

LIST OF MODIFIED FILES: 
modified:   dyn_em/module_diffusion_em.F

TESTS CONDUCTED: 
1. LES case was run with shalconv sounding to verify the change.
2. The Jenkins tests are all passing.

RELEASE NOTE: km_opt=2 and km_opt=5 tke diffusion was reduced to one third its value to match theory.

dyn_em/module_diffusion_em.F

@@ -3023,7 +3023,7 @@ SUBROUTINE horizontal_diffusion_2 ( rt_tendf, ru_tendf, rv_tendf, rw_tendf,    &
                                    config_flags,                           &
                                    tke(ims,kms,jms),                       & 
                                    msftx, msfty, msfux, msfuy,             &
-                                   msfvx, msfvy, xkhh, rdx, rdy,           &
+                                   msfvx, msfvy, xkmh, rdx, rdy,           &
                                    fnm, fnp, cf1, cf2, cf3,                &
                                    zx, zy, rdz, rdzw, dnw, dn, rho,        &
                                    .true.,                                 &
@@ -4332,7 +4332,7 @@ SUBROUTINE vertical_diffusion_2   ( ru_tendf, rv_tendf, rw_tendf, rt_tendf,   &
    If (km_opt .eq. 2) then
    CALL vertical_diffusion_s( tke_tendf(ims,kms,jms),               &
                               config_flags, tke(ims,kms,jms),       &
-                              xkhv,                                 &
+                              xkmv,                                 &
                               dn, dnw, rdz, rdzw, fnm, fnp, rho,    &
                               .true.,                               &
                               ids, ide, jds, jde, kds, kde,         &
@@ -8157,7 +8157,7 @@ SUBROUTINE vertical_diffusion_implicit(ru_tendf, rv_tendf, rw_tendf, rt_tendf,&
     DO j = j_start, j_end
     DO k = kts+1, ktf
     DO i = i_start, i_end
-        xkxavg(i,k,j) = ( fnm(k) * xkhv(i,k,j) + fnp(k) * xkhv(i,k-1,j) ) &
+        xkxavg(i,k,j) = ( fnm(k) * 2. * xkmv(i,k,j) + fnp(k) * 2. * xkmv(i,k-1,j) ) &
                        *( fnm(k) * rho (i,k,j) + fnp(k) * rho (i,k-1,j) )
     END DO
     END DO