MB-9737: New way of generating random vb UUIDs

Random vb UUIDs for failover log using the platform
functionality from platform library

Change-Id: I9ed3237a5caf6f3a9591d9346872d74b886d0cd8
Reviewed-on: http://review.couchbase.org/32568
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>