Use erlang:apply in hash_password to silence deprecation warning.

Change-Id: Id12c0442158b4da28637637b0e2e285b8a051d51
Reviewed-on: http://review.couchbase.org/35016
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>