Support attachments via stdout in the JUnit XML reader

[delatrie]

There is a convention for attaching files to the JUnit XML report via the standard output. The file path is embedded in the [[ATTACHMENT|<path>]] format:

<testcase name="foo" classname="bar">
  <system-out>
<![CDATA[
[[ATTACHMENT|./path-relative-to-junit-xml]]
[[ATTACHMENT|/absolute-path]]
]]>
  </system-out>
</testcase>

The convention is supported by many CI systems (Jenkins, Azure, etc).

We should support it as well.