nodesim: add alloc ID node metadata. (#23)

Adding any allocation ID when running nodesim on Nomad helps
debugging.

main.go

@@ -245,10 +245,11 @@ func startClient(logger hclog.Logger, buildInfo *internalSimnode.BuildInfo, cfg
 		Reserved: &structs.Resources{},
 		Links:    map[string]string{},
 		Meta: map[string]string{
-			"nodesim.id":      cfg.NodeNamePrefix,
-			"nodesim.enabled": "true",
-			"nodesim.version": buildInfo.Version,
-			"nodesim.sum":     buildInfo.Sum,
+			"nodesim.id":       cfg.NodeNamePrefix,
+			"nodesim.alloc_id": os.Getenv("NOMAD_ALLOC_ID"),
+			"nodesim.enabled":  "true",
+			"nodesim.version":  buildInfo.Version,
+			"nodesim.sum":      buildInfo.Sum,
 		},
 		CSIControllerPlugins: make(map[string]*structs.CSIInfo),
 		CSINodePlugins:       make(map[string]*structs.CSIInfo),