Fix verbosity flag not show in usage (#1425)

cmd/fission-cli/app/app.go

@@ -37,7 +37,7 @@ func App() *cobra.Command {
 		Use:  "fission",
 		Long: usage,
 		//SilenceUsage: true,
-		PreRunE: wrapper.Wrapper(
+		PersistentPreRunE: wrapper.Wrapper(
 			func(input cli.Input) error {
 				console.Verbosity = input.Int(flagkey.Verbosity)
 				return nil
@@ -53,7 +53,7 @@ func App() *cobra.Command {
 	})
 
 	wrapper.SetFlags(rootCmd, flag.FlagSet{
-		Optional: []flag.Flag{flag.GlobalServer, flag.GlobalVerbosity},
+		Global: []flag.Flag{flag.GlobalServer, flag.GlobalVerbosity},
 	})
 
 	groups := helptemplate.CommandGroups{}
@@ -64,7 +64,9 @@ func App() *cobra.Command {
 	groups = append(groups, helptemplate.CreateCmdGroup("Other Commands", support.Commands(), version.Commands()))
 	groups.Add(rootCmd)
 
-	helptemplate.ActsAsRootCommand(rootCmd, nil, groups...)
+	flagExposer := helptemplate.ActsAsRootCommand(rootCmd, nil, groups...)
+	// show global options in usage
+	flagExposer.ExposeFlags(rootCmd, flagkey.Server, flagkey.Verbosity)
 
 	return rootCmd
 }