ISPN-4681 Preloading from shared cachestore on a new node with non-share...

...d index is skipping indexing

https://issues.jboss.org/browse/ISPN-4681

This should solve ISPN-4048 and ISPN-4595 as well;  what it does is avoid indexing during preload in all cases except if we know for sure the index is not shareable (only ram falls into this category)
a couple of questions:
* can't you return true here?
* is it possible to configure multiple directory providers?