use pytest-xdist and pytest-cov for parallel testing

tox.ini

@@ -8,17 +8,15 @@ max-line-length = 120
 [testenv]
 passenv = TEST_OPSDB_HOSTNAME,TEST_OPSDB_DBNAME,TEST_OPSDB_USERNAME,TEST_OPSDB_PASSWORD
 deps =
-    coverage
+    pytest-xdist
+    pytest-cov
     flake8
     -r requirements.txt
 #install_command = pip install --pre --extra-index-url http://pip.geant.net/ --trusted-host pip.geant.net {opts} {packages}
 
 commands =
     coverage erase
-    coverage run --source inventory_provider -m pytest {posargs}
-    coverage xml
-    coverage html
-    coverage report --fail-under 80
+    pytest -n auto --cov inventory_provider -p no:checkdocs
     flake8
     sphinx-build -M html docs/source docs/build