macOS CI, cleanup in CMakeLists.txt, update of hdf5/netcdf-c/netcdf-fortran

[climbfuji]

This PR

• fixes the Travis CI setup for macOS with gcc+gfortran (version 10) and clang+gfortran
• performs some cleanup work in the top-level CMakeLists.txt
• updates HDF5, netCDF-c and netCDF-Fortran to newer versions
• turns off the tests for ESMF (since these do not pass with the Travis Linux/macOS systems when building static libraries only)

[climbfuji]

@kgerheiser does this look ok for you? It builds fine on Travis for Linux gcc+gfortran (including wgrib2), and on macOS with both gcc+gfortran (gnu-10!) and clang+gfortran. No wgrib2 build for macOS online, there is something weird going on. wgrib2 builds fine on my mac laptop. For ESMF, one needs to turn off the tests when building the static library only - fails for both Linux and macOS in Travis, and also for my Mac laptop. Not a big issue for now, and saves a lot of time. If we want to figure this out, we can turn them on for the non-Travis builds (add a flag to turn on/off these tests?).

[kgerheiser]

Looks good