[cmaes] Initial work on allowing use of MPI

The use of MPI with CMAES is now functional, though it is definitely not complete. I have a long todo list over at #246 (only some of those items are related to MPI). Note that this PR goes into cmaes-feature, not master.

I've created a CMAESMPITest, which runs CMAESTest but with MPI. I've added another travis build that uses MPI and runs CMAESMPITest. 

The test should fail right now. The error is from exceptions that are thrown by the master process. I don't want to address this failure here though; I'd like to discuss it at @246. I might actually like to exclude fixing those errors from this PR; I could comment-out the two subtests that are failing.