Post-processing on CPU devices fails when GPU device available

[valeriabarra]

If an NVIDIA GPU device is available, our post-processing tries to run there, but it would throw the following error:

ERROR: LoadError: CUDA error: unknown error (code 999, ERROR_UNKNOWN)

One way we can avoid this, is by setting the environment variable

export CLIMACOMMS_DEVICE=CPU

but a cleaner and more robust way is to pass the context to the InputOutput.HDF5Reader function.