Close netCDF files when overwriting existing files with the same name

[huard]

Description

With xarray 0.16.1, overwriting a file on disk with the same name does not clear the cache. So when opening a file with the same name, it fetches the cached file rather than the new file on disk.

Possible solutions:

• Given unique name to model outputs (.e.g uuid)
• Call .close() on all opened netCDF files when overwrite=True.

[Zeitsperre]

@huard Could this be part of the issue we have with test instability?

[huard]

It may. You could check by running tests sequentially (no xdist)