Apply InfoLogLevel to the logs in util/db_info_dumper.cc

Summary:
* Rename util/db_info_dummper.cc to util/db_info_dumper.cc
* Apply InfoLogLevel to the logs in util/db_info_dumper.cc

Test Plan: make

Reviewers: ljin, sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D27915
Check InfoLogLevel earlier in Log functions.

Summary: Check InfoLogLevel earlier in Log functions.

Test Plan: auto_roll_logger_test

Reviewers: ljin, sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D27993