Add UTCNow() function. (#3931)

This patch adds UTCNow() function which returns current UTC time.

This is equivalent of UTCNow() == time.Now().UTC()

cmd/xl-v1-object.go

@@ -1,5 +1,5 @@
 /*
- * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ * Minio Cloud Storage, (C) 2016, 2017 Minio, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,6 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"time"
 
 	"github.com/minio/minio/pkg/bpool"
 	"github.com/minio/minio/pkg/mimedb"
@@ -651,7 +650,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 	}
 
 	// Save additional erasureMetadata.
-	modTime := time.Now().UTC()
+	modTime := UTCNow()
 
 	newMD5Hex := hex.EncodeToString(md5Writer.Sum(nil))
 	// Update the md5sum if not set with the newly calculated one.