tests: plug coverage into run-tests

It makes easier to check what functions lack unit tests.

ci/coveragerc

@@ -0,0 +1,3 @@
+[run]
+source = qubes
+omit = qubes/tests/*

ci/requirements.txt

@@ -1,5 +1,6 @@
 # WARNING: those requirements are used only for travis-ci.org
 # they SHOULD NOT be used under normal conditions; use system package manager
+coverage
 docutils
 jinja2
 lxml

run-tests

@@ -7,4 +7,4 @@ PYTHONPATH="${TESTPYTHONPATH}:${PYTHONPATH}"
 export PYTHONPATH
 
 "${PYTHON}" setup.py egg_info --egg-base "${TESTPYTHONPATH}"
-"${PYTHON}" -m qubes.tests.run "$@"
+"${PYTHON}" -m coverage run --rcfile=ci/coveragerc -m qubes.tests.run "$@"