Allow configuration that enables output of results to JUnit XML file

[travi]

This format allows results to be consumed by popular CI servers.

Buster allows the override of the reporter on the command line (http://docs.busterjs.org/en/latest/modules/buster-test/options/#cmdoption-buster-test-r). Allowing us to specify the reporter (http://docs.busterjs.org/en/latest/modules/buster-test/reporters/#xml-reporter) and a file to capture the output to would enable us to leverage that output for a CI server.

[eskimoblood]

I think we can't create an reporter cause all the task does is to call the buster commands in the terminal, but we could save the result of the stdout of the process. If you think this is a way to go I would create a pull request for this.

[bakk]

Something that allows the equivalent to 'buster-test --reporter xml >testreport.xml' via grunt would be great.

[rlanore]

👍