Destroy slave after certain number of builds

[major]

It would be great if there was a way to destroy a node if it has handled a certain number of builds. For example, if a node has handled 99 builds, destroy it when the 100th build finishes so a new instance could be created. Sometimes cruft builds up on these nodes and it's helpful to destroy it every so often.

This exists in the EC2 plugin now but I don't know enough Java to make it work here in the digitalocean plugin. 😢