Setup leveldb info log file from ENV LDB_INFO_LOG

[hunterli]

Setup leveldb info log file name to environment variable LDB_INFO_LOG. Export LDB_INFO_LOG=/dev/null can disable leveldb info log.

长期运行ssdb时，data/LOG和meta/LOG文件会一直增长，通过环境变量LDB_INFO_LOG=/dev/null可以禁止此文件。