Add support to python coverage reporting

[timonwong]

Python coverage is a bit different here:
Python package file __init__.py can be empty, so upon submit, opencov cannot process the following coverage data correctly:

{
            "source": "",
            "name": "pkg/xxx/__init__.py",
            "coverage": [
                null
            ]
}

[danhper]

Hi thanks for reporting.
I do not have time to fix this right now, but I would be very happy to merge a PR.
Thank you.

[vinigfer]

@timonwong How do you configured your python project to send the report?

I did it like this:

export COVERALLS_HOST="http://localhost:4000"
export COVERALLS_REPO_TOKEN=Nk1Vck5aMnRXdlB4amFwVkplVi9Sd2JDTml2YU1CMzhib29TOEVKVQ==
coveralls

But only got a lot of "No source for ..." messages and a "Reporting 0 files" at the end.