Turn advection off for the time being (#1831)

TYPE: bug fix

KEYWORDS: KEPS PBL, advection term

SOURCE: internal and Zonato

DESCRIPTION OF CHANGES:
Problem:
Tests revealed that when model time step is relatively large on coarser grids, the scheme with advection on can become unstable causing the model to abort.

Solution:
Based on Zonato's suggestion, turning off the advection term solves the problem.

LIST OF MODIFIED FILES: 
M     phys/module_bl_keps.F

TESTS CONDUCTED: 
1. Tests show it can fix the model abort issue.
2. The Jenkins tests are all passing, no other effect on code.

phys/module_bl_keps.F

@@ -4,7 +4,7 @@ MODULE module_bl_keps
       parameter(temin=1E-4,dmin=1E-7,tpemin=1E-7,c_theta=0.09,  &
                 vk=0.4,c_mu=0.09,c1=1.44,c2=1.92,c3=1.44,c4=0.27,c5=0.08,sigma_eps=1.3) ! impose minimum values for tke similar to those of MYJ
       parameter(temax=50.,dmax=50.,tpemax=5.)
-      integer,private,parameter:: bl_keps_adv = 1
+      integer,private,parameter:: bl_keps_adv = 0
 ! -----------------------------------------------------------------------