wait-on-file: adjust the timer counter The wait performed in increment of 0.01 second, but the timer was expressed in second. So we did not wait 20s, we waited 0.2 second. Internally we adjust the counter to be expressed in centisecond. This prevent some flackyness in the test. Differential Revision: https://phab.mercurial-scm.org/D8453

packaging: add docutils as dependency The previous commit revealed that attempting to run `python setup.py build_doc` from the packaging virtualenv failed due to missing docutils package. We didn't notice this before because py2exe Windows packaging appears to use a Python from another virtualenv (which does include docutils) to invoke setup.py. I discovered this as part of implementing packaging outside of that virtualenv environment. Differential Revision: https://phab.mercurial-scm.org/D8470

setup: use sysstr() on process output Otherwise we get a str-bytes mismatch on Python 3 if an error occurs. Differential Revision: https://phab.mercurial-scm.org/D8469

automation: install latest Python versions in Linux Staying up to date. Keeping parity with the Windows environment. Differential Revision: https://phab.mercurial-scm.org/D8467

contrib: update to latest Python 2.7, 3.7, and 3.8 We would ideally update the 3.5 and 3.6 versions as well. But Python didn't generate exe installers for newer versions for some reason. Differential Revision: https://phab.mercurial-scm.org/D8466

automation: always use latest Windows AMI The old AMI isn't available any more. We seem to run into this problem every few months. Amazon (or Microsoft) appears to be removing the old AMIs when they are superseded or something. Let's give up on tracking known images and switch the image selection logic to use the latest published image. Differential Revision: https://phab.mercurial-scm.org/D8465