storage/engine: tune target_file_size_{base,multiplier}
storage/engine: tune target_file_size_{base,multiplier}

The previous settings of `target_file_size_{base,multiplier}` were
horrifically bad. A base size of `64 MB` and multiplier of `8` caused
the following target file sizes per level:

    L1   64 MB
    L2  512 MB
    L3    4 GB
    L4   32 GB
    L5  256 GB
    L6    2 TB

Combined with `level_compaction_dynamic_level_bytes` which fills from
the lowest level (L6) up, this caused excessively large
compactions. RocksDB is designed such that compactions at higher levels
only compact part of the level, but our settings were forcing compaction
of the entire level. The settings have been tuned to result in the
following target file sizes:

    L1    4 MB
    L2    8 MB
    L3   16 MB
    L4   32 MB
    L5   64 MB
    L6  128 MB

The result is a lot more files, but this is expected. For large data
storage on a node we'll need to be sure to have large open file limits.

sunya123/cockroach,petermattis/cockroach,petermattis/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,maxlang/cockroach,cockroachdb/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,maxlang/cockroach,vivekmenezes/cockroach,arjun4084346/cockroach,glycerine/cockroach,veteranlu/cockroach,glycerine/cockroach,paperstreet/cockroach,sunya123/cockroach,arjun4084346/cockroach,veteranlu/cockroach,maxlang/cockroach,vivekmenezes/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,cockroachdb/cockroach,paperstreet/cockroach,arjun4084346/cockroach,sunya123/cockroach,vivekmenezes/cockroach,sunya123/cockroach,paperstreet/cockroach,arjun4084346/cockroach,glycerine/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,maxlang/cockroach,petermattis/cockroach,petermattis/cockroach,paperstreet/cockroach,glycerine/cockroach,maxlang/cockroach,glycerine/cockroach,maxlang/cockroach,cockroachdb/cockroach,maxlang/cockroach,petermattis/cockroach,petermattis/cockroach,arjun4084346/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,veteranlu/cockroach,cockroachdb/cockroach,veteranlu/cockroach,glycerine/cockroach,vaibhavarora/cockroach,arjun4084346/cockroach,glycerine/cockroach,petermattis/cockroach,veteranlu/cockroach,glycerine/cockroach,vaibhavarora/cockroach,sunya123/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,petermattis/cockroach,vivekmenezes/cockroach,maxlang/cockroach,vivekmenezes/cockroach,paperstreet/cockroach,sunya123/cockroach,vaibhavarora/cockroach,veteranlu/cockroach,vivekmenezes/cockroach,sunya123/cockroach,cockroachdb/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,sunya123/cockroach