Optional more granular reporting for JUnit reports

[tosky]

What would you like to be added:

#509 changed the format of the JUnit reports to be more granular. A statement at the end of the Caveats section says

If needed, I could add a knob to make this high-granularity opt-in.in the end

This request is about introducing such knob to allow people to use the previous, less granular reporting format.

Why is this needed:

This potential need was already highlighted in the commit which changed the format, as highlighted above. I'd like to add that in the project I contribute, OpenStack Kubernetes Operators, we are starting to collect the results of KUTTL tests in a consistent way for internal reporting. The way each operator structured its tests is to have to have a basic mapping of 1-1 between tests and features. We don't want nor need to mark each step for reporting. So instead of having to post-process the JUnitXML file, it would be nice if kuttl could produce also (with some flag) the report in the old format.