api: Bucket notification add filter rules check and validate. (#2272)

These filtering techniques are used to validate
object names for their prefix and suffix.

logger.go

@@ -19,6 +19,7 @@ package main
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"os"
 	"runtime"
 	"runtime/debug"
@@ -52,6 +53,8 @@ type logger struct {
 	// Add new loggers here.
 }
 
+var errLoggerNotEnabled = errors.New("requested logger type is not enabled")
+
 // sysInfo returns useful system statistics.
 func sysInfo() map[string]string {
 	host, err := os.Hostname()