CI error parser needs to ignore configure errors

now that configure is run with -v (at least in some configs), the CI posts logs with a lot of useless information to gerrit - see last-but-one integration attempt in https://codereview.qt-project.org/50221. the consequence is that people think "eh, this is all bullshit which doesn't concern me" - and restage their broken changes.

the error parser must ignore everything which comes from configure tests.
caveat: it cannot ignore everything from configure, as the qmake compile can legitimately fail. if you don't find a way to reliably detect that, i can add a message to configure to say when it is done with bootstrapping qmake.