Dispose idle server provisioned by different sources

For user that use openstack mainly for Jenkins and related automation. It can make sense to cleanup dangling machines by openstack plugin. Just today, my slave died and job was not able to cleanup slaves it started (started by SUT, not Jenkins). If would be great if plugin can be made responsible for disposing these resources as well.

Servers provision can have a metadata field instructing plugin to perform cleanup:
- After certain date. (This server should live for a couple of hours. It is certainly useless if running after 24h)
- Ties server lifetime to Jenkins entity (slave, build, etc). (This is a server provisioned for purposes of a build and once the build is done/gone it is useless).

If documented users can take advantage of that in custom automation.