Add sanitized landsat2.nc

@rouault
> [landsat2.nc.zip](https://github.com/qgis/QGIS/files/1352514/landsat2.nc.zip)
> "gdal_translate -of NETCDF landsat.tif landsat2.nc" will not work as expected
> since the driver doesn't support creating subdatasets. I have used ncdump +
> manual changing of _FillValue to 0 + ncgen to recreate it. Hopefully it
> should work (untested) Result attached