[FIXED JENKINS-35160] - Job deletion: Wait up to 15 seconds for interrupted...

[FIXED JENKINS-35160] - Job deletion: Wait up to 15 seconds for interrupted builds to complete (#2789)

* [FIXED JENKINS-35160] Wait up to 15 seconds for interrupted builds to complete

- Also now aware of concurrent builds

* [JENKINS-35160] Tests are good, they catch bugs

* [JENKINS-35160] We should do the interrupt for any Item not just Jobs

* [JENKINS-35160] s/DeleteBlocker/ItemDeletion/g

Left over references before I settled on a better name

* [JENKINS-35160] Switch to Failure for better HTML rendering

* [JENKINS-35160] Align the i18n key with owning class