Switch to testenv:functional
Switch to testenv:functional

This brings our tox.ini files inline with other OpenStack projects.

Change-Id: I5c5fd1ef79e6ab08088ce58e45b593715d0e28ed
Depends-On: I376e51824c46f9b5eb4a4cff01aaa176632087dd
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack/openstack-ansible-apt_package_pinning,openstack/openstack-ansible-apt_package_pinning