Collect coverage information for integration tests in CI

[tyll]

There is some tooling to provide coverage information for integration tests: https://github.com/linux-system-roles/network/blob/main/tests/get_total_coverage.sh

Currently, this information is not yet used in the CI/not reported anywhere. It would be great to also get this information. Ideally, test-harness would support calling it. Another options is to run the tests in containers on Travis.