python-subunit 1.4.3+ requires 'extras' otherwise an error
occures:
"'run --slowest' is not a stestr command."
Switch to using self-signed-certificates-operator as the
self signed functionality has been removed from
tls-certificates-operator charm *1
*1 2cb418cd2e
Change-Id: I47139a8d3203b4dc0953bc64491a9f58533d6a10
Following changes are done as part of this patch:
* Sync global tox, requirements.txt, test-requirements
from release-tools project
* Resolve flake errors
* Restructure unit tests directory
Liam Young