Pass back the status dict from BFGS

[denizokt]

Relevant file: moe/optimal_learning/python/python_version/optimization.py optimize() method of LBFGSBOptimizer.

if you check out like multistart_hyperparameter_optimization, it can pass back a status dict. and in the REST interface, that status dict is written into the response.

it could be good to pass the status dict back that BFGS returns. and/or if 'warnflag' is not zero, log the dict contents or maybe only do this at the multistart level. anyway I'd at least ticket this; don't have to do it now.