Job DSL: Ignore old jobs in reality, delete in imagination

[noidi]

When developing the pipeline, we want the Jenkins jobs to match our configuration files exactly. But in production, we don't want to lose a job and its valuable history when someone renames it in a configuration file.

We should set "Action for removed jobs" to "Delete" in imagination and "Ignore" in reality.

This depends on solita/ansible-role-solita.jenkins#6.