[JENKINS-17751] set upstream builds to original builds of promotions

When Parametrized Trigger is used with [Promoted Builds] (https://wiki.jenkins-ci.org/display/JENKINS/Promoted+Builds+Plugin), the upstream build that can be seen from downstream builds is set to not the original build like "ProjectA build number # 1", but a promotion like "ProjectA/promotion/PromotionA build number # 1". This makes Jenkins unable to create a link from the downstream build to the original upstream build.

This patch changes builds used for UpstreamCause from promotions to promotions.

I reported the details in [JENKINS-17751] (https://issues.jenkins-ci.org/browse/JENKINS-17751).