Add junit xml output to test script

[gut]

Use hphp/test/run --xml to get an junit-like xml output. Useful on e.g
Jenkins as it can plot those results to a time series, so a regression
is easily spotted.

[gut]

@mxw or whoever can review this

[fredemmott]

Can you use a more generic format instead (eg Test Anything Protocol/TAP)? I don't like the idea of adding an option that's meant to emulate a tool that none of us use.

If there isn't a more tool-agnostic format that can be used instead, please rename the option to --junit-xml or similar, not just --xml, in case we have other needs in the future.

[fredemmott]

as well as my previous comment, if you stick with an XML-based format, use one of the built-in XML libraries instead of just concatenating/interpolating/printf'ing strings.

[gut]

Ok, I'll take a closer look. Thanks for the hints