Built-By should take Jenkin's BUILD_USER_ID variable into account

[quidryan]

When the Build User Vars Plugin is used, jenkins provides BUILD_USER_ID environment variable of the user who kicked off the job. This would be a better indicator than System.getProperty('user.name').

I would propose the CI providers be the ones who contribute the Built-By field, defaulting to user.name. They are the ones explaining the execution environment.