Merge remote-tracking branch 'remotes/philmd-gitlab/tags/python-next-20200531' into...

Python queue:

* migration acceptance test fix
* introduce pylintrc & flake8 config
* various cleanups (Python3, style)
* vm-test can set QEMU_LOCAL=1 to use locally built binaries
* refactored BootLinuxBase & LinuxKernelTest acceptance classes

https://gitlab.com/philmd/qemu/pipelines/151323210
https://travis-ci.org/github/philmd/qemu/builds/693157969

# gpg: Signature made Sun 31 May 2020 17:37:35 BST
# gpg:                using RSA key FAABE75E12917221DCFD6BB2E3E32C2CDEADC0DE
# gpg: Good signature from "Philippe Mathieu-Daudé (F4BUG) <[email protected]>" [full]
# Primary key fingerprint: FAAB E75E 1291 7221 DCFD  6BB2 E3E3 2C2C DEAD C0DE

* remotes/philmd-gitlab/tags/python-next-20200531: (25 commits)
  tests/acceptance: refactor boot_linux to allow code reuse
  tests/acceptance: refactor boot_linux_console test to allow code reuse
  tests/acceptance: allow console interaction with specific VMs
  tests/acceptance/migration.py: Wait for both sides
  tests/migration/guestperf: Use Python 3 interpreter
  tests/vm: allow wait_ssh() to specify command
  tests/vm: Add ability to select QEMU from current build
  tests/vm: Pass --debug through for vm-boot-ssh
  python/qemu/qtest: Check before accessing _qtest
  python/qemu/qmp: assert sockfile is not None
  python/qemu/qmp: use True/False for non/blocking modes
  python/qemu: Adjust traceback typing
  python/qemu: fix socket.makefile() typing
  python/qemu: remove Python2 style super() calls
  python/qemu: delint; add flake8 config
  python/qemu: delint and add pylintrc
  python/qemu/machine: remove logging configuration
  python/qemu/machine: add kill() method
  python: remove more instances of sys.version_info
  scripts/qmp: Fix shebang and imports
  ...

Signed-off-by: Peter Maydell <[email protected]>