I verified locally that this avoids skipping all of the
faketime-dependent unittests. The Travis CI logs will have to be
investigated for all of the other docker images on which distros we may
need to apply a similar fix.
This is an attempt at updating all docker configurations by simply
replacing the `python` packages with `python3`. The Travis CI will let
us know if this works.
These dockerfiles can be used to run taskwarrior's test suite on the
respective platforms using the following commands:
$ cd taskwarrior.git
$ docker build -t test-tw-fedora28 -f test/docker/fedora28 .
$ docker run test-tw-fedora28
For ubuntu, replace fedora28 with ubuntu1604.
