Merge branch 'ndk/machinefiles/disable-MPICH_GNI_DYNAMIC_CONN' (PR #2026

)

Add environment variable to cori-knl
setenv MPICH_GNI_DYNAMIC_CONN=disabled
Only for mpilib=mpt (not for Intel MPI)
This has shown to reduce initialization time -- especially in the atmosphere init.
It may also benefit other machines, but starting with cori-knl.
[BFB]

cime/config/acme/machines/config_machines.xml

@@ -466,6 +466,10 @@
     <env name="OMP_PROC_BIND">spread</env>
     <env name="OMP_PLACES">threads</env>
   </environment_variables>
+
+  <environment_variables mpilib="mpt">
+    <env name="MPICH_GNI_DYNAMIC_CONN">disabled</env>
+  </environment_variables>
   <environment_variables mpilib="impi">
     <env name="I_MPI_FABRICS">ofi</env>
     <env name="I_MPI_OFI_PROVIDER">gni</env>