tests: Add tox.ini file and migrate to pytest
Related swh/infra/ci-cd/swh-jenkins-jobs#1247 (closed) Related swh-environment#1261 (closed)
Test Plan
tox
Migrated from D572 (view on Phabricator)
Related swh/infra/ci-cd/swh-jenkins-jobs#1247 (closed) Related swh-environment#1261 (closed)
tox
Migrated from D572 (view on Phabricator)