Allow pipelining coverage data from browsers

[bitinn]

When we need to report coverage data to a third-party service, such as coveralls, we would like to rely on zuul command to pipe us the coverage result from our sauce labs tests (allow us to specify which browser's test result to use, for example.)

Currently we have to install mochify in addition to zuul, in order to use phantomjs to run the same tests to produce coverage result.

And for one of my project, vdom-parser, this becomes a problem because we rely on DOMParser API in browsers, which phantomjs only has partial support.

So we ended up needing polyfill for DOMParser API, and because it's not spec compliant, we are unable to achieve 100% test coverage, even though on supported browsers we do have 100% coverage.

TL;DR: follow up on #174, please help us to get coverage data from real browsers and allow us to pipe them to coverage reporting services.

[cesarandreu]

Since you wanna get code coverage from the tests running on the actual browser (and not phantomjs), can't you hit the http://localhost:58700/__zuul/coverage/download endpoint?

[bitinn]

I can try, to pull stats archive using curl and then unzip it and then pipe it to coveralls. Not sure if it would work on sauce labs though.

[defunctzombie]

I would review a PR or other improvements to make this work for you and other users. I don't recall the details of the coverage additions but if something is missing we can add it.