tavis ci is warning about usage of pytest feature that is deprecated

[yazug]

=============================== warnings summary =============================== errata_tool/tests/test_add_builds.py::TestAddBuilds::test_builds_empty_no_release /home/travis/build/yazug/errata-tool/errata_tool/tests/test_add_builds.py:35: PytestDeprecationWarning: The 'message' parameter is deprecated. (did you mean to use match='some regex' to check the exception message?) Please comment on https://github.com/pytest-dev/pytest/issues/3974 if you have concerns about removal of this parameter. message='Need to specify a release'): errata_tool/tests/test_add_builds.py::TestAddBuilds::test_builds_new_advisory /home/travis/build/yazug/errata-tool/errata_tool/tests/test_add_builds.py:51: PytestDeprecationWarning: The 'message' parameter is deprecated. (did you mean to use match='some regex' to check the exception message?) Please comment on https://github.com/pytest-dev/pytest/issues/3974 if you have concerns about removal of this parameter. message='Cannot add builds to unfiled erratum'): -- Docs: https://docs.pytest.org/en/latest/warnings.html

[yazug]

@ktdreyer appears the travisCI is now failing on this.

Job #637.3 on python 3.6 is now failing https://travis-ci.org/red-hat-storage/errata-tool/jobs/557951272

[yazug]

feature was deprecated in pytest 4.1

[ktdreyer]

I read that a future version of setuptools is going to deprecate the "test" subcommand entirely. On my other Python projects, I'm switching them all over to tox and tox-travis. We should do the same for python-errata-tool.

[ktdreyer]

I have a work-in-progress branch that switches us over to tox. My branch fails without https://github.com/red-hat-storage/errata-tool/pull/165, so I've merged that one now.

[ktdreyer]

Here's my change that switches to tox: https://github.com/red-hat-storage/errata-tool/pull/190