fix: unwrapping issues with os.Is* functions (#10949)

reduces  3 stat calls, reducing the
overall startup time significantly.

cmd/object-api-putobject_test.go

@@ -409,7 +409,7 @@ func testObjectAPIMultipartPutObjectStaleFiles(obj ObjectLayer, instanceType str
 		files, err := ioutil.ReadDir(tmpMetaDir)
 		if err != nil {
 			// Its OK to have non-existen tmpMetaDir.
-			if os.IsNotExist(err) {
+			if osIsNotExist(err) {
 				continue
 			}