MB-9737: New way of generating random vb UUIDs

Use the platform functionality from platform library

Change-Id: I6325d1ffeb3a1aef43d7fbb80f97dfbcf1123afd
Reviewed-on: http://review.couchbase.org/32346
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>