component/*/test*cfg: reorganise now that python3 is default

test.cfg becomes the python3 version
a new test-py2.cfg is introduced
test-py3.cfg is removed

cf slapos commit cc7f36a0 (component/defaults: use python3 by default, 2022-08-27)
6 jobs for feat/mroonga-up
Status Job ID Name Coverage
  External
failed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

failed ERP5.StandaloneDeploymentScriptTest-Debian.Buster.Master

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Buster

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Stretch

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Stretch