Changed CrosscheckFingerprints hashing to linked hashing

[tmelman]

Issue: CrosscheckFingerprints produces results in a different order each time.

Change: Switched from HashMap and HashSet to Java's LinkedHashMap and LinkedHashSet, respectively

Intended result: Produce stable sorted output.

Issue: #1854

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[serge2016]

Great!

[lbergelson]

@tmelman As a heads up, Collectors.toSet() is cursed by HashSet, so you may have to replace instances of stream collection with Collectors.toCollection(LinkedHashSet::new)) or continue to suffer the horrors in non-deterministic behavior.

[lbergelson]

I looked at this a bit more, it seems like there is instability built in at the start since FingerPrintChecker.fingerprintFiles() builds an unsorted map from the output of a parallel and unpredictable process. I think it's going to require a more complicated change than just changing the other sets to linked sets. Either change the inputs to return their results in order, or sort the maps according to some criteria.

[lbergelson]

I think we either need to change it so the input maps are built as the result of Futures instead of being added to the concurrent map as the are built. The errors are actually handled this way so it wouldn't be that hard to change.

The other option would be to pick an arbitrary sort order and sort the input maps after they're built and then maintain that order.