JENKINS-25011: find projects by their full name.

https://wiki.jenkins-ci.org/display/JENKINS/Hierarchical+projects+support

Using `Jenkins.getInstance().getItem(...)` only returns `TopLevelItem`, which
means that it was previously impossible to use the `Promoted Build Parameter`
with folders. To make that work better, use full names, and let autocomplete
return full names.
Since in the latter case you are not really completing the supplied string anyway, may as well just say

    if (job.getFullName().contains(value)) {

and let people type in any subset they like.