Bug fix: use mpiexec for MPI programs

Even for a run with a single MPI process, otherwise execution will not
work on some systems (jean-zay).

Inst_eddies/Tests/short_tests.json

@@ -224,10 +224,12 @@
 	[
 	    ["mkdir", "SHPC"],
 	    [
+		"$mpiexec", "-n", "1",
 		"$build_dir/Inst_eddies/test_set_max_speed",
 		"$PWD/Get_1_outerm/SHPC"
 	    ]
-	]
+	],
+	"stdout": "test_set_max_speed_stdout.txt"
     },
     {
         "required":
@@ -247,10 +249,12 @@
 	[
 	    ["mkdir", "SHPC"],
 	    [
+		"$mpiexec", "-n", "1",
 		"$build_dir/Inst_eddies/test_set_max_speed",
 		"$PWD/Get_1_outerm_noise_2_8/SHPC"
 	    ]
-	]
+	],
+	"stdout": "test_set_max_speed_stdout.txt"
     },
     {
         "input": "&main_nml min_amp = 0./\n",
@@ -316,9 +320,10 @@
         "title": "Nearby_extr",
         "command":
 	[
-	  "$build_dir/Inst_eddies/test_nearby_extr",
-	  "$PWD/Inst_eddies_loop/SHPC_cyclo_all_dates"
-	]
+            "$mpiexec", "-n", "1", "$build_dir/Inst_eddies/test_nearby_extr",
+	    "$PWD/Inst_eddies_loop/SHPC_cyclo_all_dates"
+	],
+	"stdout": "test_nearby_extr_stdout.txt"
     },
     {
         "description": "test_set_all_outerm with periodicity.",