BuildStepOperationTest.testConfigurationWithoutDbc works with Mailer builder that doesn't support DataBoundContructor.
But mailer stats to support DataBoundconstructor since mailer-1.6 (which is bundled since jenkins-1.544).

Let's create a test extension instead.

This is also a fix for https://github.com/jenkinsci/build-timeout-plugin/commit/b4d9acc2d7519ff05c35b3f5f84c29c93a9ac8ac.