[script] fix output when no arguments are specified (#5551)

When no arguments are provided to script/test, the script prints $1:
unbound variable and exits without printing the usage
information. This is due to the set -u at the top.

This commit has a small fix so that this usage is presented with the
usage information. Also, it prints an error when it detect an unknown
command.

script/test

@@ -423,7 +423,7 @@ main()
 {
     envsetup "$@"
 
-    if [[ -z $1 ]]; then
+    if [[ -z ${1:-} ]]; then
         print_usage 1
     fi
 
@@ -469,6 +469,10 @@ main()
                 shift
                 do_untar "$@"
                 ;;
+            *)
+                echo
+                echo -e "${COLOR_FAIL}Warning:${COLOR_NONE} Ignoring: '$1'"
+                ;;
         esac
         shift
     done