CBLT-159:  fix up "usage" statement

Change-Id: Ie77a9e727c94eba47ead236836179d0e50a96db6
Reviewed-on: http://review.couchbase.org/38332
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>