CBD-1425:  use curl instead of wget.  macosx comes with curl

Change-Id: I123ae4f073fff80c52dc18f2a29164a03c82c562
Reviewed-on: http://review.couchbase.org/40422
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>