Coverage tests fail on Windows CI with coverage 5.0

[rly]

Error is:

(tox) λ tox -e coverage-py35
coverage-py35 recreate: C:\Users\Ryan\Documents\NWB\hdmf\.tox\coverage-py35
coverage-py35 installdeps: -rrequirements-dev.txt, -rrequirements.txt
WARNING: Discarding $PYTHONPATH from environment, to override specify PYTHONPATH in 'passenv' in your configuration.
coverage-py35 develop-inst: C:\Users\Ryan\Documents\NWB\hdmf
WARNING: Discarding $PYTHONPATH from environment, to override specify PYTHONPATH in 'passenv' in your configuration.
coverage-py35 installed: certifi==2019.11.28,chardet==3.0.4,codecov==2.0.15,colorama==0.4.3,coverage==5.0.2,entrypoints==0.3,filelock==3.0.12,flake8==3.7.9,h5py==2.10.0,-e git+https://github.com/hdmf-dev/hdmf.git@9471e5ca425ade3a85ad949a463c5d716088dcd0#egg=hdmf,idna==2.8,importlib-metadata==1.3.0,mccabe==0.6.1,more-itertools==8.0.2,numpy==1.18.1,packaging==20.0,pandas==0.25.3,pluggy==0.13.1,py==1.8.1,pycodestyle==2.5.0,pyflakes==2.1.1,pyparsing==2.4.6,python-dateutil==2.8.1,pytz==2019.3,requests==2.22.0,ruamel.yaml==0.16.5,ruamel.yaml.clib==0.2.0,scipy==1.4.1,six==1.13.0,toml==0.10.0,tox==3.14.3,urllib3==1.25.7,virtualenv==16.7.9,zipp==0.6.0
coverage-py35 run-test-pre: PYTHONHASHSEED='53'
coverage-py35 run-test: commands[0] | coverage run test.py -u
Traceback (most recent call last):
  File "test.py", line 18, in <module>
    from tests.coloredtestrunner import ColoredTestRunner, ColoredTestResult
ImportError: No module named 'tests'
Coverage.py warning: No data was collected. (no-data-collected)
ERROR: InvocationError for command 'C:\Users\Ryan\Documents\NWB\hdmf\.tox\coverage-py35\Scripts\coverage.EXE' run test.py -u (exited with code 1)

There appears to be a change in how the python path is handled. This happens for python 3.5, 3.6, 3.7, and 3.8, and only on Windows - Mac and Linux are OK. This also only happens when upgrading to coverage 5.0.2 from 4.5.4.

This seems possibly related to nedbat/coveragepy#862

[rly]

The workaround is to use "python -m coverage run (etc)" instead of "coverage run (etc)".

Also, I tried to debug the issue here: nedbat/coveragepy#862 (comment)