fixed golint warnings for cbauth

Change-Id: I5c059c88b353fc8c901913c282addbf46124aebe
Reviewed-on: http://review.couchbase.org/44201
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>