tox: Don't set basepython in testenv
tox: Don't set basepython in testenv

Turns out doing this overrides the basepython for every 'py{version}'
implicit target, meaning py35, py36 etc. will use the same Python 3.x
version. We don't want that so set basepython manually.

This will hopefully be a non-issue when the gate bumps to Bionic.

Change-Id: I8d47f9ede4e9d1d221f6643135407ad2d5cea282
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>

openstack/oslo.log