Multiple leaves are not handled correctly with DIST

When multiple caches are leaving at the same time(i.e. the diff between jgroups views is more than one address), Infinispan ends up with an inconsistent hash function: it is aware about nodes that are no longer present in the cluster.
The root cause of the problem is in DistributionManagerImpl.rehash(...):

• the list of leavers is determined as follows:
  Address leaver = MembershipArithmetic.getMemberLeft(oldMembers, newMembers);
• this method always assumes a single leaver, but there can be many.

Unit test attached.