support for customized actions

Hi! 

I made some changes to your plugin to support the execution of customized Groovy actions when the regex is matched. The idea is not to only restart the job but also to do something about it like disconnecting the agent, cleaning the disk, etc. I created two script examples here: https://github.com/deccico/periodic-reincarnation-plugin/tree/master/scripts but virtually anything can be done. 

Please let me know what you think.