store user name with token for future use with audit log

Change-Id: I741653cfff7d5a65659e89f6f6418671b6cd3761
Reviewed-on: http://review.couchbase.org/43065
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>