consider Aggregation iterator to allow for runtime when getting next granule

[jbfaden]

I have a bug which would be difficult to fix in the CDAWeb granule iterator, where it's hasNext method believes there is a last file in the interval

http://localhost:8280/HapiServer/hapi/data?id=ALOUETTE2_AV_LIM&time.min=1967-01-14T23:59:59.967Z&time.max=1967-01-15T12:59:04.000Z&parameters=Time,height

but there's a file-not-found error when the last file is retrieved.

I'm tempted to catch this exception and simply move on, issuing the runtime error to the console.