MB-6972: Fix make yum work by using createrepo after signing

Change-Id: I9583bed68fd68a985a921363116861bae7a022be
Reviewed-on: http://review.couchbase.org/36806
Reviewed-by: Eric Limare <eric.limare@couchbase.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Eric Limare <eric.limare@couchbase.com>