Reduce debug logging on default levels in error log

There is some excessive logging in RocksDB.
This is written apparently every time when CHECK TABLE is run on a RocksDB table:

2018-04-17 23:05:16 140080091559680 [Note] CHECKTABLE t1: Checking table t1

And this when an index is created (possibly even many times per index?):

2018-04-17 23:08:55 140080091559680 [Note] RocksDB: Begin index creation (0,257)