tests: port test-wireproto.py to Python 3 A little bit of output churn because we now get b'' prefixes on output in both 2 and 3, but for this test I'm more comfortable knowing that we're using bytestrs everywhere. Differential Revision: https://phab.mercurial-scm.org/D3510

tests: port test-context.py to Python 3 This is a weird "minimally invasive" port. I think there's room to do better here, but I'm also not sure how often we'll touch this code... Differential Revision: https://phab.mercurial-scm.org/D3509