Add support for POST commit coverage runs

Modeled on how keystone does it.

Change-Id: Idad4f854f1bfb915a48ff69988553810a76accc0
Signed-off-by: Peter Portante <peter.portante@redhat.com>

tox.ini

@@ -16,6 +16,13 @@ deps =
   -r{toxinidir}/test-requirements.txt
 commands = nosetests test/unit {posargs}
 
+[testenv:cover]
+setenv = VIRTUAL_ENV={envdir}
+         NOSE_WITH_COVERAGE=1
+         NOSE_COVER_BRANCHES=1
+         NOSE_COVER_HTML=1
+         NOSE_COVER_HTML_DIR={toxinidir}/cover
+
 [tox:jenkins]
 downloadcache = ~/cache/pip