Display coverage report

... for easy reference. Also make sure old data is purged.

Also adds .coveragerc which is present in the other repos.

Change-Id: Ifee20fc38e9c8bb04c20ff4e690e652b9256d46f

.coveragerc

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

tox.ini

@@ -27,12 +27,14 @@ commands =
 deps = {[testenv]deps}
     coverage
 setenv =
-    PYTHON=coverage run --source $project --parallel-mode
+    PYTHON=coverage run --source oslo_rootwrap --parallel-mode
 commands =
+    coverage erase
     stestr run {posargs}
     coverage combine
     coverage html -d cover
     coverage xml -o cover/coverage.xml
+    coverage report --show-missing
 
 [testenv:venv]
 commands = {posargs}