Temporary header should not be save to meta when making snapshot files

**Describe the bug**
When make snapshot files in OLAPEngine::_create_snapshot_files, the temp new header is construct to describe the snapshot files. But  the temp new header is save to replace the ref table's original header, and this may cause lose of version information and schema change status info.

**How to fix**
the temp new header should not be save to meta.

