[CI] Report pytest --junitxml results when tests fail

[areusch]

Right now we don't do junit reports when tests fail, so the Tests tab isn't super helpful outside of telling you test runtime. We should fix this so it becomes more useful. Modify the jenkinsfile to always invoke junit even if the shell script fails.

@mikepapadim will take a look
cc @leandron @jroesch @denise-k

[mikepapadim]

On-going PR in #8757

[driazati]

we have this in Jenkins now for every test step, closing