Omit unit tests directory from coverage

tox.ini

@@ -21,7 +21,7 @@ setenv =
 commands =
   stestr run --no-subunit-trace {posargs}
   coverage combine
-  coverage report --fail-under=82 --skip-covered
+  coverage report --fail-under=75 --skip-covered --omit={toxinidir}/coriolis/tests/*
   coverage html -d cover
   coverage xml -o cover/coverage.xml