Create a better way to chain log cleaners

From Stack's review of HBASE-2223:

Why this implementation have to know about other implementations? Can't we do a chain of decision classes? Any class can say no? As soon as any decision class says no, we exit the chain.... So in this case, first on the chain would be the ttl decision... then would be this one... and third would be the snapshotting decision. You don't have to do the chain as part of this patch but please open an issue to implement.