Re-add index_per_partition but as deprecated
Re-add index_per_partition but as deprecated

Summary:
index_per_partition should have deprecated deprecated instead of being removed. It is causing backward compatibility issues.
Closes https://github.com/facebook/rocksdb/pull/2173

Differential Revision: D4910947

Pulled By: maysamyabandeh

fbshipit-source-id: 5c52939381847d232ede6866606f67f2b4b857ae

vmx/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,vmx/rocksdb,Andymic/rocksdb,vmx/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,Andymic/rocksdb,bbiao/rocksdb,vmx/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,vmx/rocksdb,bbiao/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,bbiao/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,bbiao/rocksdb,vmx/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,vmx/rocksdb,Andymic/rocksdb,Andymic/rocksdb