Don't change comm flags when there is only 1 MPI rank

the *cuda/aware* keyword is set to *off* while any of the *comm*

keywords are set to *device*\ , the value for these *comm* keywords will

be automatically changed to *host*\ . This setting has no effect if not

running on GPUs. CUDA-aware MPI is available for OpenMPI 1.8 (or later

versions), Mvapich2 1.9 (or later) when the "MV2\_USE\_CUDA" environment

variable is set to "1", CrayMPI, and IBM Spectrum MPI when the "-gpu"

flag is used.

running on GPUs or if using only one MPI rank. CUDA-aware MPI is available

for OpenMPI 1.8 (or later versions), Mvapich2 1.9 (or later) when the

"MV2\_USE\_CUDA" environment variable is set to "1", CrayMPI, and IBM

Spectrum MPI when the "-gpu" flag is used.

----------

#ifdef KOKKOS_ENABLE_CUDA

  int nmpi = 0;

  MPI_Comm_size(world,&nmpi);

  // if "cuda/aware off" and "comm device", change to "comm host"

  if (!cuda_aware_flag) {

  if (!cuda_aware_flag && nmpi > 1) {

    if (exchange_comm_classic == 0 && exchange_comm_on_host == 0) {

      exchange_comm_on_host = 1;

      exchange_comm_changed = 1;