The role name is misleading. It's not fetching stestr output, it's
fetching subunit output.
Add a note to the README explaining what it does and that it's not using
fetch-subunit-output on purpose.
Use "{{ zuul.project.src_dir }}" instead of
"src/{{ zuul.project.canonical_name }}".
Change-Id: I1b5ab65f9697ec184969ca7899fb40294cdb853c