audit logging infrastructure and logging of login success/failure

Change-Id: Ida67c6b01c1d417b95667ec2452842964b1cbd70
Reviewed-on: http://review.couchbase.org/43067
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>