CBD-1249:  platform names are: centos-6-x64, centos-6-x86, ubuntu-6-x64, ubuntu-6-x86, etc.

Change-Id: Ib06e05c92f031ae95fffe51a3d8578735e1e7a3d
Reviewed-on: http://review.couchbase.org/39062
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>