tox.ini: restore commands line, fix tabs vs. spaces (#224)

The `commands` line was accidentally(?) removed entirely in
57f716ed, so tox no longer actually ran any tests (only flake8).
This restores it, with the codestyle bit removed obviously. It
also fixes two lines where a tab was used instead of spaces.

Signed-off-by: Adam Williamson <awilliam@redhat.com>