Force creating of ROOT Streamers at begin of job

The code which constructs ROOT Streamers is not thread safe. Unfortunately,
Streamers normally get created the first time they are needed which would
be too late for our case. This change forces all Streamers to be created,
even if we do not need them for this job.
Merge pull request #2074 from Dr15Jones/makeStreamersEarly

Multithreaded framework -- Force creating of ROOT Streamers at begin of job