add annotation for rocksdb config option

Signed-off-by: xinxin shu <xinxin.shu@intel.com>
enable info_log_level config option for rocksdb

Signed-off-by: xinxin shu <xinxin.shu@intel.com>
Merge pull request #2202 from xinxinsh/enable-rocksdb-log-level

Enable rocksdb log level

Reviewed-by: Sage Weil <sage@redhat.com>