Fix pflag binding for demo cmd

Summary:
TSIA. The cmd object passed into PersistentPreRun is the lowermost
level cmd. So the flag lookup on the command only finds the local flags but
not inherited flags. This fixes the lookup for the demo commands.

Test Plan: Build a px binary and tried to deploy demo apps.

Reviewers: michelle

Reviewed By: michelle

Signed-off-by: Vihang Mehta <vihang@pixielabs.ai>

Differential Revision: https://phab.corp.pixielabs.ai/D12006

GitOrigin-RevId: 1f8cdfb

Author: vihangm

src/pixie_cli/pkg/cmd/demo.go

@@ -67,7 +67,13 @@ var DemoCmd = &cobra.Command{
 	Use:   "demo",
 	Short: "Manage demo apps",
 	PersistentPreRun: func(cmd *cobra.Command, args []string) {
-		viper.BindPFlag("artifacts", cmd.PersistentFlags().Lookup("artifacts"))
+		// This pre run might be run from a subcommand. To bind the correct flag, we should check
+		// the persistent flags on both the current command and the parent.
+		if cmd.PersistentFlags().Lookup("artifacts") != nil {
+			viper.BindPFlag("artifacts", cmd.PersistentFlags().Lookup("artifacts"))
+			return
+		}
+		viper.BindPFlag("artifacts", cmd.Parent().PersistentFlags().Lookup("artifacts"))
 	},
 	Run: func(cmd *cobra.Command, args []string) {
 		utils.Info("Nothing here... Please execute one of the subcommands")