Merge bitcoin#8141: Continuing port of java comparison tool

ff2dcf2 Tests: Edit bloated varint test and add option for 'barely expensive' tests (mrbandrews)
12c5a16 Catch exceptions from non-canonical encoding and print only to log (mrbandrews)
291f8aa Continuing port of java comptool (mrbandrews)
8c9e681 Tests: Rework blockstore to avoid re-serialization. (mrbandrews)

Author: laanwj