The change does 3 things:
1. It limits RocksDB to 256 file descriptors instead of unlimited
2. It includes the fd limit in its estimation for total file descriptors needed
3. It raises the system fd limit if possible before we open rocksdb but accounting for the 256 limit we added
Former-commit-id: 1447288209c5e7daf8a1203511fc262500ebe5e1
9e5b7aaaa9