AvailabilityException and AvailabilityMode are in the wrong package

AvailabilityException and AvailabilityMode are in package org.infinispan.partionhandling, instead of org.infinispan.par*ti*tionhandling.

For AvailabilityException, we could create a new exception in the proper package and make the old one extend the new one, but I'm not sure how we should handle AvailabilityMode.