Specific Build Selector fixes

Aside from fixing [JENKINS-19693] (https://issues.jenkins-ci.org/browse/JENKINS-19693), the specific build will also allow to use permalinks (e.g. lastSuccessfulBuild).

If you take the example of a build pipeline, trigerring job after job and want to reuse the same artifact in multiple jobs of that pipeline, you can use a variable in the specific build field which turns out to be a build parameter (String). The value is provided by the job that triggers the build and fill it with the build number of another job so that the same artifact can be reused. However, when a job alone is triggered and not as part of a build pipeline or build flow, it is convenient to be able to use a permalink like lastSuccessfulBuild as the default value for that build parameter.