test: stabilize test-wireproto-exchangev2.t flaky output When running the test suite with multiple processes, we often get flaky outputs, like here: https://ci.octobus.net/job/MercurialPy2/267/console ``` - received frame(size=0; request=1; stream=2; streamflags=; type=command-response; flags=eos) add changeset cd2534766bec add changeset e96ae20f4188 add changeset caa2a465451d + received frame(size=0; request=1; stream=2; streamflags=; type=command-response; flags=eos) ``` Instead of simply sorting the clone and pull output, I saved the output in a separate file and checked the `received frame` messages on one side and then the rest of the output on the other side. This way we conserve the order of messages as it seems important. Differential Revision: https://phab.mercurial-scm.org/D5897