CBIDXT-94: unit test cases for logger.

Change-Id: I08fc7751c8439c048eaec0407ffd8cde239dcf13
Reviewed-on: http://review.couchbase.org/39344
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>