CBLT-283:  use "s3cmd get" instead of wget

Change-Id: If5e37d0a33588d294e06a8f9b51ed6dbbe56fe1e
Reviewed-on: http://review.couchbase.org/36762
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>