[JENKINS-22857] DSL support for post build cleanup the workspace using the Workspace Cleanup Plugin

Closed previous pull request #189 as I had some problems with git and had to fork again. 
- Added examples
- Fixed unit tests by using with from Specification class 
- extracted common functionality into base class as it supported by the current DSL implementations. There might be more when the DSL and/or plugin evolves in the future.