add unit test and documentation for finalizers (#2509)

* add unit test and documentation for finalizers
* error msg with lower case and cover sync case
* try to avoid adding json-patch dependency
* use Update to remove finalizer
* changing status and finalizer during create
* do not call Delete() twice

pkg/util/util.go

@@ -152,6 +152,17 @@ func IsEqualIgnoreOrder(a, b []string) bool {
 	return reflect.DeepEqual(a_copy, b_copy)
 }
 
+// Iterate through slice and remove certain string, then return cleaned slice
+func RemoveString(slice []string, s string) (result []string) {
+	for _, item := range slice {
+		if item == s {
+			continue
+		}
+		result = append(result, item)
+	}
+	return result
+}
+
 // SliceReplaceElement
 func StringSliceReplaceElement(s []string, a, b string) (result []string) {
 	tmp := make([]string, 0, len(s))