Add UTCNow() function. (#3931)

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

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

cmd/signature-v2_test.go

@@ -1,3 +1,19 @@
+/*
+ * 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.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package cmd
 
 import (
@@ -6,7 +22,6 @@ import (
 	"net/url"
 	"sort"
 	"testing"
-	"time"
 )
 
 // Tests for 'func TestResourceListSorting(t *testing.T)'.
@@ -30,7 +45,7 @@ func TestDoesPresignedV2SignatureMatch(t *testing.T) {
 	}
 	defer removeAll(root)
 
-	now := time.Now().UTC()
+	now := UTCNow()
 
 	testCases := []struct {
 		queryParams map[string]string