[Catapult] Fixed vinn_unittests
[Catapult] Fixed vinn_unittests

Converted vinn_unittests to be py3 compatible, mainly on decoding/encoding.

Those tests has been failing but somehow LUCI was reporting pass:
https://ci.chromium.org/ui/p/catapult/builders/try/Catapult%20Linux%20Tryserver%20Py3/274/overview

Bug: chromium:1221663
Change-Id: Ice89a496329c3bfd8d8a69813b56a9123d2be5fa
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/3068002
Commit-Queue: Wenbin Zhang <45ad8a1ff616a38a2202fd35571df81897c5f14f@google.com>
Reviewed-by: John Chen <334fbfbb4df7c78f091ea1b77c69ca6ac731a3f3@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult