Guard against haunted netCDF4/HDF5 combo

[benjaminhwilliams]

On some platforms, it seems importing h5py before netCDF4 leads to errors like

OSError: [Errno -101] NetCDF: HDF error: '/path/to/HDF5/file.h5'

when trying to open an HDF5 file as an Xarray dataset.

This might be fixed by proper packaging, since it seems to happen when Pip installs incompatible h5py and netCDF4 packages (motivation for CondaForge feedstock, perhaps), but for now the generally accepted workaround seems just to be importing netCDF4 first.