CBLT-319:  fix S3 URLs for SGW dashboards

Change-Id: I43d5b99d0ea8f2aea4fcb8dc49cd5dbe680ab7fa
Reviewed-on: http://review.couchbase.org/39030
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>