[RooFit] Fix race condition when running tutorial tests.
[RooFit] Fix race condition when running tutorial tests.

The python and c++ versions of the roofit tutorials compile the same file,
which sometimes breaks one of the two when they run in parallel.

olifre/root,root-mirror/root,olifre/root,karies/root,karies/root,karies/root,olifre/root,karies/root,olifre/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,karies/root,olifre/root,karies/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,olifre/root,root-mirror/root,karies/root