travis: switch to other Boost PPA and test 1.53 and 1.55

I don't think is what you want to be doing... the root rank does not know what the errors for the other ranks are, so really you are only testing the error on the first rank.  Note that the return value of `mpirun` is really what counts here, not what each ranks `main` is returning (for `ctest`).  I'm not sure what `mpirun` returns if only one rank's main signals a error, so perhaps we should do an MPI max reduce on `result` and have all ranks return that.