Upddate tox config

- Removes py3 env since we don't run unit tests
- Update requirements to use stestr and coverage
- Update tox.ini to use stestr

Change-Id: Iecb18a3e616173217b7edb756dcaabd8df009629
diff --git a/tox.ini b/tox.ini
index 60be8ec..6d79734 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.1.0
-envlist = py3,pep8
+envlist = pep8
 skipsdist = True
 ignore_basepython_conflict=true
 
@@ -13,7 +13,7 @@
    PYTHONWARNINGS=default::DeprecationWarning
 deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py test --slowest --testr-args='{posargs}'
+commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
 commands = flake8 {posargs}
@@ -22,7 +22,14 @@
 commands = {posargs}
 
 [testenv:cover]
-commands = python setup.py test --coverage --testr-args='{posargs}'
+setenv =
+    {[testenv]setenv}
+    PYTHON=coverage run --source ironic_tempest_plugin --parallel-mode
+commands =
+    stestr run {posargs}
+    coverage combine
+    coverage htlm -d cover
+    coverage xml -o cover/coverage.xml
 
 [testenv:docs]
 commands = python setup.py build_sphinx