fix_sst_dump_for_old_sst_format

Summary:
1. fix segment error when dumping old sst format (no properties nor stats)
2. Enable dumpping old sst format

Test Plan:
Generate block based sst file with "properties", and one with "stats" and one without neither.
Read it using sst_dump

Reviewers: ljin, igor, yhchiang, dhruba, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D21837