Enhancement : Need a handler for Interrupt/Cancel lifecycle

[milindraut]

For most of the transcoder job, we would like to sent the NATs message when the job is cancelled or interrupted(nomad -> floop -> transcoder_proxy -> transcoder). This will allow us to manage/send the correct status message to the NATs when job is cancelled. Currently status for complete, progress and failed can be sent - but would also need the handler for "Cancel".