[FIXED JENKINS-20559 and JENKINS-19454] - hudson.Launcher bugfix and additional wrapper

Summary:
* A fix for NPE in hudson.Launcher.ProcSrater::envs() 
* A DecoratedLauncher code, which is being duplicated by many plugins (Custom Tools, etc.)
* A test for JENKINS-20559, which uses a DecoratedLauncher

The last bullet is a reason, why these changes have been merged into a single PR