cleanup: fix use of _CheckNodeOnline

A few cases of wrong variable name.

Reviewed-by: amishchenko

lib/cmdlib.py

@@ -2333,7 +2333,7 @@ class LUActivateInstanceDisks(NoHooksLU):
     self.instance = self.cfg.GetInstanceInfo(self.op.instance_name)
     assert self.instance is not None, \
       "Cannot retrieve locked instance %s" % self.op.instance_name
-    _CheckNodeOnline(self, instance.primary_node)
+    _CheckNodeOnline(self, self.instance.primary_node)
 
   def Exec(self, feedback_fn):
     """Activate the disks.
@@ -2714,7 +2714,7 @@ class LUShutdownInstance(LogicalUnit):
     self.instance = self.cfg.GetInstanceInfo(self.op.instance_name)
     assert self.instance is not None, \
       "Cannot retrieve locked instance %s" % self.op.instance_name
-    _CheckNodeOnline(self, instance.primary_node)
+    _CheckNodeOnline(self, self.instance.primary_node)
 
   def Exec(self, feedback_fn):
     """Shutdown the instance.
@@ -5527,7 +5527,7 @@ class LUExportInstance(LogicalUnit):
     self.instance = self.cfg.GetInstanceInfo(instance_name)
     assert self.instance is not None, \
           "Cannot retrieve locked instance %s" % self.op.instance_name
-    _CheckNodeOnline(self, instance.primary_node)
+    _CheckNodeOnline(self, self.instance.primary_node)
 
     self.dst_node = self.cfg.GetNodeInfo(
       self.cfg.ExpandNodeName(self.op.target_node))