add bmc_version for nodes without iDrac

data/grid5000/sites/luxembourg/clusters/granduc/nodes/granduc-12.json

@@ -11,7 +11,7 @@
     "vendor": "Dell Inc.",
     "version": "2.7.0"
   },
-  "bmc_version": "unknown",
+  "bmc_version": "1.33",
   "chassis": {
     "manufacturer": "Dell Inc.",
     "name": "PowerEdge 1950",