Migrate to stestr

This patch updates tox.ini to use stestr instead of testr.

Change-Id: I6be57c0c90d7711c172243b9de43034735334de7
diff --git a/tox.ini b/tox.ini
index f168afd..70b834d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -10,7 +10,9 @@
    VIRTUAL_ENV={envdir}
    PYTHONWARNINGS=default::DeprecationWarning
 deps = -r{toxinidir}/test-requirements.txt
-commands = python setup.py test --slowest --testr-args='{posargs}'
+commands =
+  stestr run {posargs}
+  stestr slowest
 
 [testenv:pep8]
 commands = flake8 {posargs}
@@ -19,7 +21,18 @@
 commands = {posargs}
 
 [testenv:cover]
-commands = python setup.py test --coverage --testr-args='{posargs}'
+setenv =
+  {[testenv]setenv}
+  PYTHON=coverage run --source octavia_tempest_plugin --parallel-mode
+whitelist_externals =
+  find
+commands =
+  find octavia_tempest_plugin -type f -name "*.pyc" -delete
+  coverage erase
+  stestr run {posargs}
+  coverage combine
+  coverage html -d cover
+  coverage xml -o cover/coverage.xml
 
 [testenv:docs]
 deps =