Add test of caching to test harness.

tests/pio_write_run.in

 #! @SHELL@
 set -e
 LOG="${LOG-pio_write.log}"
-if [ @ENABLE_GRIB@ = yes ]; then
-  mpi_task_num="${mpi_task_num-4}"
-  suffix="${suffix-grb}"
+if [ @ENABLE_GRIB@ != yes ]; then
+  # skip tests for unsupported formats
+  exit 77
+fi
+mpi_task_num="${mpi_task_num-4}"
+suffix="${suffix-grb}"
+if [ "@USE_MPI@" = yes ]; then
+  variations="-qcache-redists"
+else
+  unset variations
+fi
+for variation in "" $variations ; do
   exec 5>&1 6>&2 >"$LOG" 2>&1
   ../libtool --mode=execute \
     @MPI_LAUNCH@ \
-    -n ${mpi_task_num} ${tool_wrap} ./pio_write ${pio_write_args}
+    -n ${mpi_task_num} ${tool_wrap} ./pio_write ${pio_write_args} ${variation}
   exec 2>&6 1>&5 5>&- 6>&-
   ../libtool --mode=execute \
     ${tool_wrap} ./cksum_read example_0.${suffix} example_0.cksum
   ../libtool --mode=execute \
     ${tool_wrap} ./cksum_read example_1.${suffix} example_1.cksum
   \rm "$LOG"
-else
-  # skip tests for unsupported formats
-  exit 77
-fi
+done
 #
 # Local Variables:
 # mode: sh