Fix for issue JENKINS-20037

 https://issues.jenkins-ci.org/browse/JENKINS-20037

A performance regression was introduced by 46f1770 which cause a reduction in performance by an order of magnitude (4 min builds taking 40 min).

This pull reverts that change and brings build back to previous performance levels.  

46f1770 should be re-examined to find a better way of accomplishing its goal without such a drastic impact on performance of the plugin.