Tweak jbosstools-promote job to allow omission of core

As discussed previously via email, I would like a small change to the jbosstools-promote job [1].
We publish RedDeer to urls such as:
http://download.jboss.org/jbosstools/updates/development/luna/core/reddeer/0.8.0.M1/
http://download.jboss.org/jbosstools/updates/stable/luna/core/reddeer/0.7.0/

The job currently supports having NONE for luna/mars. But there is no way to omit the "core" part. For us it really has no meaning, and the simpler the url the better, so it would be nice if this could be empty.

This most probably just requires something similar to this:

if [[ ${TARGET_PLATFORM} == "NONE" ]]; then TARGET_PLATFORM=""; fi

in https://github.com/jbosstools/jbosstools-build-ci/blob/master/publish/promote.sh#L71
And then a new option for NONE for the PARENT_FOLDER parameter in the jenkins job.

If you agree this is fine, I can make it happen (create PR for jbosstools-build-ci and update the job).

[1] https://jenkins.mw.lab.eng.bos.redhat.com/hudson/view/DevStudio/view/DevStudio_Master/job/jbosstools-promote/