Improve coverage rules for Qt projects

The coverage reports (see for example https://jenkins.qa.ubuntu.com/job/ubuntu-system-settings-online-accounts-utopic-amd64-ci/18/cobertura/client_OnlineAccountsClient/ ) do not exclude the moc auto-generated files, and therefore lead to a lower coverage score.

I propose adding these two options to the gcovr invocation: '--exclude=.*/moc_.*.cpp' '--exclude=.*moc'