[coverage] Add coverage tests with avocado and replace nosetests

[arif-ali]

Replacing nosetests with avocado coverage.

Adding it as a separate test for latest python also helps with testing new versions of python, which we didn't pick up in the past

There was a bug in avocado that wouldn't work and was discussed in avocado-framework/avocado#5610 and resolved. It is due to be back-ported to the LTS we are using, so adding this a sa draft to get it going and others to review

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[packit-as-a-service]

Congratulations! One of the builds has completed. 🍾

You can install the built RPMs by following these steps:

• sudo yum install -y dnf-plugins-core on RHEL 8
• sudo dnf install -y dnf-plugins-core on Fedora
• dnf copr enable packit/sosreport-sos-3668
• And now you can install the packages.

Please note that the RPMs should be used only in a testing environment.