Is it possible, or are there tools available to allow you, to import or convert a legacy Jenkins job build definition into a TFS 2017 build definition. I'm not looking to convert the job to a Jenkins job within TFS, but simply use the steps contained in the Jenkins job to create a new build definition.
If the steps contained in jenkins job you are meaning just as the following screen shows which you can specify the details of the job.
Unfortunately, it's not able to directly covert this to a TFS build definition. There is no such kind tool could do this. It's only able to Export/Import TFS vNext Build Definition itself. You have to manually convert jenkins job build definition to TFS build definition.