Switch to stestr

According to Openstack summit session [1] stestr is
maintained project to which all Openstack projects
should migrate.
Let's switch it then.

[1] https://etherpad.openstack.org/p/YVR-python-pti

Change-Id: I856024f8b66f5edaf40ae7b798fce21c43d021e7
diff --git a/tox.ini b/tox.ini
index d966308..bba0a64 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,8 +9,11 @@
 setenv =
    VIRTUAL_ENV={envdir}
    PYTHONWARNINGS=default::DeprecationWarning
+   OS_LOG_CAPTURE={env:OS_LOG_CAPTURE:true}
+   OS_STDOUT_CAPTURE={env:OS_STDOUT_CAPTURE:true}
+   OS_STDERR_CAPTURE={env:OS_STDERR_CAPTURE:true}
 deps = -r{toxinidir}/test-requirements.txt
-commands = python setup.py test --slowest --testr-args='{posargs}'
+commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
 commands =
@@ -23,7 +26,14 @@
 commands = {posargs}
 
 [testenv:cover]
-commands = python setup.py test --coverage --testr-args='{posargs}'
+setenv =
+    {[testenv]setenv}
+    PYTHON=coverage run --source neutron_tempest_plugin --parallel-mode
+commands =
+    stestr run --no-subunit-trace {posargs}
+    coverage combine
+    coverage html -d cover
+    coverage xml -o cover/coverage.xml
 
 [testenv:docs]
 commands = python setup.py build_sphinx