Update rocksdb default options

[Jouzo]

No description provided.

[prasannavl]

Should also resolve #3098 (with the max file open targets).

Currently, we'll have 3 DBs, one managed by LevelDB, 2 rocksdb instances - one internal, and the other through vsdb. With 256 per instance, expect this to stay under most default common distro defaults of 1024.

We'll be upwards of 700+, but as long as other system resources haven't taken up too much, should work reasonably.

Note: This is just to keep it operational, but production servers are still expected to use a larger file count as larger DBs just require larger limits.