Add step to run smoke tests

[gctucker]

Once the step to build a kernel image is complete, the next part is to run kvm-xfstests with the smoke set of tests. This is a relatively small set which can take around 15min to complete on a decent machine. It's a good compromise to have some useful coverage without running the full set of tests which would take many hours.

During development, it's also possible to hard-code a couple of test names to get results much quicker rather than the whole smoke set.

• [x] Step added to add another call kvm-xfstests to run the smoke tests
• [x] Verified manually in the log output that the tests were run as expected
• [x] Overall status reported to the API, still with a single fstests node

[alexandrasp]

• I am investigating how to access the VM and get the result.xml during the runtime using the template and subprocess with multiple commands.
• Manually I am already able to see the tests running, so when the tests finish I can join the VM and see the results file.

[gctucker]

I don't think it's necessary to get the XML file out of the VM, checking the output is enough for now to know the tests were run as expected. We'll see the details of the logs when parsing the XML results.