Support for multiple test summaries in a single JUnit report

[lyricsboy]

When running tests against multiple destinations (e.g. iOS 8 + 9 simulators), xcodebuild produces a separate TestSummaries.plist for each destination. It would be super cool to aggregate these into a single JUnit report.

I propose flattening all the test runs into a single array of testsuites in the resulting XML. If we do that, we'll need to have some metadata at the testsuite level to distinguish one run of a target from another on a different destination.

Using a properties element allows us to add arbitrary key-value pairs to the testsuite.

[lyricsboy]

Here's a branch where I've added some properties to the testsuite: master...lyricsboy:lyricsboy/multiple-test-summaries

Check it out and let me know what you think.

[nikolaykasyanov]

It would be great to have this! @lyricsboy 👍

[CraigLn]

I'm hoping this isn't lost, but would be great it if could be added in. @lyricsboy possible to open a PR?

[lyricsboy]

@CraigLn see #20. I have not yet tested this in a real scenario, but if you are interested in it, please do so and let us know if it works as desired.