Cleanup error output

oz/main.go

@@ -199,22 +199,23 @@ func getSandboxById(id int) (*daemon.SandboxInfo, error) {
 
 func handleKill(c *cli.Context) {
 	if len(c.Args()) == 0 {
-		fmt.Errorf("Need a sandbox id to kill\n")
+		fmt.Fprintf(os.Stderr, "Need a sandbox id to kill\n")
 		os.Exit(1)
 	}
 	if c.Args()[0] == "all" {
 		if err := daemon.KillAllSandboxes(); err != nil {
-			fmt.Errorf("Kill command failed:", err)
+			fmt.Fprintf(os.Stderr, "Kill command failed:", err)
+			os.Exit(1)
 		}
-		return
 	}
 	id, err := strconv.Atoi(c.Args()[0])
 	if err != nil {
-		fmt.Errorf("Could not parse id value %s\n", c.Args()[0])
+		fmt.Fprintf(os.Stderr, "Could not parse id value %s\n", c.Args()[0])
 		os.Exit(1)
 	}
 	if err := daemon.KillSandbox(id); err != nil {
-		fmt.Errorf("Kill command failed:", err)
+		fmt.Fprintf(os.Stderr, "Kill command failed:", err)
+		os.Exit(1)
 	}
 
 }