Make sure xarray times out when request takes too long

[huaracheguarache]

Today I experienced that seaice.metsis-api.met.no didn't load. Local testing revealed that this was due to an issue with the thredds server as the following command wasn't able to return a dataset:

xr.open_dataset('https://thredds.met.no/thredds/dodsC/metusers/thomasl/v2p1/beau/osisaf_beau_sie_daily.nc')

In order to deal with this sort of failure we need a way to specify how long xarray or the backend netCDF4 tries to fetch the file from the server before it times out. It doesn't look like this functionality is provided by xarray or the backend netCDF4-python. We need to look for alternative ways to deal with this.