tempfile.NamedTemporaryFile behaving as /vsimem and eating all the machine memory
While working on https://github.com/cogeotiff/rio-cogeo/pull/75 we noticed strange behaviors with `vsimem` driver (this could be a GDAL but TBH).
1. When using `tempfile.NamedTemporaryFile()` Rasterio uses `vsimem` driver
Here I was expecting Rasterio/GDAL to behave as `tempfile` was a regular file.
2. When closing a `vsimem` (`MemoryFile` or `tempfile`) we observe a huge memory surge when working with big images.
Tested on Mac OS and linux with python 3.7 (gdal 2.4 and 2.3)