Exit with error properly and fix lint check

cmd/wwctl/main.go

@@ -1,12 +1,16 @@
 package main
 
 import (
+	"os"
+
 	"github.com/hpcng/warewulf/internal/app/wwctl"
 )
 
 func main() {
 	root := wwctl.GetRootCommand()
 
-	//nolint:errcheck
-	root.Execute()
+	err := root.Execute()
+	if err != nil {
+		os.Exit(255)
+	}
 }