Without this comma, tox runs the standard testenv instead of this one.
This is due to how tox calculates factors (parts of a testenv name) and
checks for their existence [1].

[1] https://github.com/tox-dev/tox/issues/3219



Change-Id: I3fc33a26b0d7f057d7bd6a094fc2ceeaa88f177b
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>