remove remaining Docker containers when tests are interrupted

[d9pouces]

Remove remaining Docker containers when tests are interrupted.

Avoid the use of a global variable, but assume that Docker calls are all working without exception.

Does not work with tox < 3 (the required tox_cleanup hook is missing).

[hans2520]

@d9pouces is this going to be merged?

Looking to upgrade to tox-docker v2 (which seems to be needed to use the latest MySQL versions such as v8 or 5.7.31), but the change in section naming is problematic without automatic cleanup.

In previous versions of tox-docker, a container name wasn't specified, and so a auto-generated name by docker was created. This would leave a container behind, but it wouldn't prevent a new test run from starting since it would use a new auto-generated name.

Now that the section name also serves as the container name -- if that container isn't cleaned up afterwards, the same container name will be used on subsequent runs, and it will fail to start if there is a docker conflict.

The CLI argument to prevent cleanup of containers on exit should also probably be added as an explicit option in the ini file as well.

[d9pouces]

from my point of view, everything is ok for merging it

[dcrosta]

Thanks! Just posted https://pypi.org/project/tox-docker/3.0.0/ with this fix; I decided to remove tox 2.x support, which is > 3 years old at this point.

[dcrosta]

Does this address the issue in #37, specifically the case where an exception is raised from within tox-docker's tox_runtest_pre function? (I can test this later, just curious if you happened to do so while working on this, @d9pouces)