Update tox configuration

Author: Dany9966

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 4.0.2
-envlist = py3,pep8
+envlist = py3,pep8,cover
 skipsdist = True
 
 [testenv]
@@ -21,7 +21,7 @@ setenv =
 commands =
   stestr run --no-subunit-trace {posargs}
   coverage combine
-  coverage report --skip-covered
+  coverage report --fail-under=82 --skip-covered
   coverage html -d cover
   coverage xml -o cover/coverage.xml