ci: allow mpirun oversubscription

Problem: amd64 runners using OpenMPI were failing with messages like
the following:

```
There are not enough slots available in the system to satisfy the 4
  slots that were requested by the application
```

The problem seems to be the GitHub Runners do not have many
resources.

As a workaround, add an option to oversubscribe resources.

Author: jameshcorbett

cmake/SCR_ADD_TEST.cmake

@@ -1,7 +1,7 @@
 FUNCTION(SCR_LAUNCHER_PARMS procs)
     IF(${SCR_RESOURCE_MANAGER} STREQUAL "NONE")
         SET(test_launcher "mpirun" PARENT_SCOPE)
-        SET(test_param "-np ${procs}" PARENT_SCOPE)
+        SET(test_param "-np ${procs} ${MPIRUN_FLAGS}" PARENT_SCOPE)
     ELSEIF(${SCR_RESOURCE_MANAGER} STREQUAL "SLURM")
         SET(test_launcher "srun" PARENT_SCOPE)
         SET(test_param "-t 5 -N ${procs} -n ${procs}" PARENT_SCOPE)

src/test/checks_run.sh

@@ -39,6 +39,12 @@ ulimit -c unlimited
 source /etc/profile.d/modules.sh
 module load mpi
 
+if mpirun -V | grep "Open MPI"; then
+  # without this flag, in GitHub Action Runners, mpirun will complain that there
+  # aren't enough resources
+  ARGS="-DMPIRUN_FLAGS='--map-by :OVERSUBSCRIBE' ${ARGS}"
+fi
+
 
 POSTCHECKCMDS=":"
 # Enable coverage for $CC-coverage build