CBD-1354:  use new shorter names for windows build jobs:
             cs_mst_win3208
             cs_mst_win6408

Change-Id: Ib7bff44b442eef50add6fe5a49d114c6ffe0e09d
Reviewed-on: http://review.couchbase.org/36294
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>