Implement [JENKINS-23665] Parameter to select alias ...

Hope this will be helpful also for others.
If you want to do me a favor, promote it into the next LTS as well.

If I may ask: 
Is there a reason that Jenkins ... sorry ... Winstone is locked to the 8.x branch of Jetty?

I'm referring to the block of code from line 187-line 208. It seems unnecessary for fixing the linked issue — is all of this required to prevent regressions in existing setups?

Note that I'm not a committer to this repo, so my opinion can be safely ignored ;-)