packer: Handle errors with executing the CLI

packer.go

@@ -50,7 +50,12 @@ func main() {
 		os.Exit(1)
 	}
 
-	exitCode, _ := env.Cli(os.Args[1:])
+	exitCode, err := env.Cli(os.Args[1:])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error executing CLI: %s\n", err.Error())
+		os.Exit(1)
+	}
+
 	plugin.CleanupClients()
 	os.Exit(exitCode)
 }