make sure nvidia-probe always outputs valid json, even if nothing is present

Former-commit-id: c3e16696

roles/slurm-common/scripts/nvidia-probe.py

@@ -55,5 +55,7 @@ try:
         output=json.dumps(deviceList)
         print output
 except OSError:
+        output=json.dumps([])
+        print output
 #if nvidia-smi is not installed on computer then this error is thrown by subprocess.Popen
         sys.exit(0)