Fix up tox -e cover to use coverage

Change-Id: I4516a958efd4b14a6d0f9f8a7763311f134c5215

.converagerc

@@ -0,0 +1,7 @@
+[run]
+branch = True
+source = oslo_limit
+omit = oslo_limit/tests/*
+
+[report]
+ignore_errors = True

test-requirements.txt

@@ -7,6 +7,8 @@ hacking>=3.0.1,<3.1.0 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0
 stestr>=1.0.0 # Apache-2.0
 
+coverage!=4.4,>=4.0 # Apache-2.0
+
 # Bandit security code scanner
 bandit>=1.7.0,<1.8.0 # Apache-2.0
 

tox.ini

@@ -34,7 +34,13 @@ commands =
   sphinx-build -W --keep-going -b html doc/source doc/build/html
 
 [testenv:cover]
-commands = python setup.py test --coverage --coverage-package-name=oslo_limit --testr-args='{posargs}'
+setenv =
+  PYTHON=coverage run --source oslo_limit --parallel-mode
+commands =
+  stestr run --slowest {posargs}
+  coverage combine
+  coverage html -d cover
+  coverage report
 
 [testenv:releasenotes]
 allowlist_externals = rm