Fail build option

Right now the plugin will only mark a build unstable if a bug threshold is reached. This PR adds another option to fail a build if a separate bug threshold is reached. So for instance if there are 5 bugs the build is marked unstable, but if there are 10, the build is failed.

Failing the build takes precedence over marking it unstable. If the bug threshold for unstable is bigger than the threshold for failing, it won't matter as the build will be marked failed.