Switch from bullseye to CTC++ for coverage

We currently use bullseye for coverage reports, this is for historical reasons: we originally tried CTC++, found it had parsing errors in the code we tried to test, so we switched to bullseye which did not have such errors.

After some time of using bullseye we now understand that both tools more or less are working the same way and have equal chance of parsing errors in our sources. We should switch back to CTC++ because that is more widely supported within Nokia.

This blocks most other coverage related tasks since we should not waste time fixing up problems with a tool we will stop using.