heal: Add healing support for bucket, bucket metadata files. (#3252)

This patch implements healing in general but it is only used
as part of quickHeal().

Fixes #3237

cmd/object-errors.go

@@ -324,3 +324,23 @@ type NotImplemented struct{}
 func (e NotImplemented) Error() string {
 	return "Not Implemented"
 }
+
+// Check if error type is ObjectNameInvalid.
+func isErrObjectNameInvalid(err error) bool {
+	err = errorCause(err)
+	switch err.(type) {
+	case ObjectNameInvalid:
+		return true
+	}
+	return false
+}
+
+// Check if error type is ObjectNotFound.
+func isErrObjectNotFound(err error) bool {
+	err = errorCause(err)
+	switch err.(type) {
+	case ObjectNotFound:
+		return true
+	}
+	return false
+}