Summary:
tools/check_format_compatible.sh will check a newer version of RocksDB can open option files generated by older version releases. In order to achieve that, a new parameter "--try_load_options" is added to ldb. With this parameter set, if option file exists, we load the option file and use it to open the DB. With this opiton set, we can validate option loading logic.
Closes https://github.com/facebook/rocksdb/pull/2178

Differential Revision: D4914989

Pulled By: siying

fbshipit-source-id: db114f7724fcb41e5e9483116d84d7c4b8389ca4