add category command line option

[mr-c]

To record other axis like python35 or similar

Should propagate down to the TestResult.__init__ for use in TestResult.create_test_case by passing to junit_xml.TestCase as the category attribute.

[mr-c]

Inspired by common-workflow-language/cwltool#505 (comment)

[manu-chroma]

I will try to solve this one.

[manu-chroma]

[manu-chroma]

category attribute is not available in the latest release. I am using classname attribute and this is what the output looks like for a single conformance test.

The last release was almost a year ago. kyrus/python-junit-xml#43