fix: typo in optimize for QSUB2, use pathos.multiprocessing for outer loop


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/mystic/mystic@728 968178ea-60bd-409e-af13-df8a517b6005
Merge branch 'master' of https://github.com/uqfoundation/mystic