Minor changes

clusterman/commands/node.py

@@ -36,6 +36,9 @@ def check(timeout=0.1):
     if os.path.exists(nodes_path):
         with open(nodes_path) as f:
             nodes=json.load(f)
+    else:
+        print("Please perform a scan before")
+        exit(0)
     if not nodes == None:
         fail=False
         for ip in nodes: