ISPN-4822 MassIndexer is not ClusteredQuery friendly

https://issues.jboss.org/browse/ISPN-4822

Introduced an optional configuration parameter for the MassIndexer called __flushPerNode__ (false by default). 

When enabled, will purge and flush (commit) indexes on a per node basis. This is necessary for ClusteredQuery, where each node has an independent index.

I'm aware that we already have lots of properties in query, but the issue here is that it's not possible to reliably detect if an index is shared or not by only looking at configuration.