Generate coverage reports

[dblnz]

It would be nice to get some test coverage reports to know where we are in terms of testing.

[dblnz]

We now have this report that shows the test coverage for kvm.
The next step is to extend this to cover mshv and windows.
The logical steps would be:

• run tests on kvm, mshv and windows as separate jobs
• store the results
• Separate job to merge all the coverage data and generate a report.
  I'm not sure yet, but we might need to save other artifacts beside the coverage data.