Added code coverage section to tox

Defined cover in tox.ini and added .coveragerc configuration
consistent with other projects

http://lists.openstack.org/pipermail/openstack-dev/2015-October/076193.html

Change-Id: I426f1081425ca9f8ea4297c665632954cc74bb8d

.coveragerc

@@ -0,0 +1,8 @@
+[run]
+branch = True
+source = automaton
+omit = automaton/tests/*
+
+[report]
+ignore_errors = True
+precision = 2

.gitignore

@@ -37,6 +37,7 @@ htmlcov/
 .testrepository/
 .tox/
 .coverage
+cover
 .cache
 nosetests.xml
 coverage.xml

tox.ini

@@ -34,3 +34,6 @@ commands = {posargs}
 [flake8]
 show-source = True
 exclude=.venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build
+
+[testenv:cover]
+commands = python setup.py test --coverage --testr-args="{posargs}"