Prevent randomUUID contention on Elasticsearch commands

It is known that java.util.UUID.randomUUID is slow, part of it is serialized which creates contention when used in concurrence.

Some call are comming from third parts (mongo, es) others are from Nuxeo code (repository document id, es command id).

When using large worker pool size the contention is limiting, mostly from the org.nuxeo.elasticsearch.commands.IndexingCommand to generates its id.

Replacing this id by an atomic long sequence sounds to be working fine and remove the contention.