Out of order events produced when using the MassIndexer with async backend

When using async indexing backend on DIST caches with shared index (InfinispanIndexManager), the MassIndexer fails to re-index all the entries, if it is run from a node that is not
the indexing master.

Normally the operation sequence of the MassIndexer in the above configuration, for a two node cluster is:

• Purge the index
• Send index job to node A and to node B
• Flush

Given the backend is async, all index commands are sent to the master RPC-wise asynchronously, and so a reorder can occur and produce like:

• Send index job to node A
• Purge
• Send index job to node B
• Flush

Causing previously re-indexed entries to be wiped