This creates a single ADIOS target instead of both an MPI and serial target in the same build. This is primarily motivated by the various incompatibilities that arise when both serial and parallel versions of dependencies exist in the runtime environment at the same time. Most HPC module environments actually explicitly prohibit this. With this change, the MPI and serial library versions will need to be done in two separate builds. Similarly, all the dependencies (HDF5, NetCDF, etc.) that have both a parallel and serial version available will need to use their serial version for the serial build and their parallel version for the MPI build.
