Add support for timeouts for locks (#4377)

cmd/object-api-errors.go

@@ -305,6 +305,15 @@ func (e ObjectTooSmall) Error() string {
 	return "size of the object less than what is expected"
 }
 
+// OperationTimedOut - a timeout occurred.
+type OperationTimedOut struct {
+	Path string
+}
+
+func (e OperationTimedOut) Error() string {
+	return "Operation timed out: " + e.Path
+}
+
 /// Multipart related errors.
 
 // MalformedUploadID malformed upload id.