Fix python3.9 testing

Latest setuptools has deprecated the use of setup.py commands like
`setup.py testr`. For some reason python3.9 hangs and fails to work at
all when you run `setup.py testr`. Switch to running testr directly and
not bother debugging this too aggressively as this functionality is
going away eventually.

Change-Id: I3ad9e0c00990fbb7d26b03674833666f32b3bcae

tox.ini

@@ -11,8 +11,11 @@ basepython = python3
 install_command = pip install {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
+allowlist_externals = bash
 commands =
-  python setup.py testr --slowest --testr-args='{posargs}'
+  bash -c "[ -d .testrepository ] || testr init"
+  testr run -- {posargs}
+  testr slowest
 
 [tox:jenkins]
 sitepackages = True
@@ -22,8 +25,10 @@ commands = flake8
 
 [testenv:cover]
 setenv = VIRTUAL_ENV={envdir}
+allowlist_externals = bash
 commands =
-  python setup.py testr --coverage
+  bash -c "[ -d .testrepository ] || testr init"
+  testr --coverage
 
 [testenv:venv]
 commands = {posargs}