Add test coverage support

Prints out results on console and puts HTML report in `coverage-html`.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

script/test-versions

@@ -19,8 +19,9 @@ for version in $DOCKER_VERSIONS; do
     --rm \
     --privileged \
     --volume="/var/lib/docker" \
+    --volume="${COVERAGE_DIR:-$(pwd)/coverage-html}:/code/coverage-html" \
     -e "DOCKER_VERSION=$version" \
     --entrypoint="script/dind" \
     "$TAG" \
-    script/wrapdocker nosetests "$@"
+    script/wrapdocker nosetests --with-coverage --cover-branches --cover-package=compose --cover-erase --cover-html-dir=coverage-html --cover-html "$@"
 done