fix image unset

modify "target" to "tagret"

Change-Id: I80674b23804b26430aed13b5e6c6dc2b240771cd

Author: zheng yin

openstackclient/image/v2/image.py

@@ -933,7 +933,7 @@ def take_action(self, parsed_args):
                       'propret': propret, 'proptotal': proptotal})
             raise exceptions.CommandError(msg)
         elif tagret > 0:
-            msg = (_("Failed to unset %(target)s of %(tagtotal)s tags.")
+            msg = (_("Failed to unset %(tagret)s of %(tagtotal)s tags.")
                    % {'tagret': tagret, 'tagtotal': tagtotal})
             raise exceptions.CommandError(msg)
         elif propret > 0: