iotests: alphabetize standard imports

iotests: alphabetize standard imports

I had to fix a merge conflict, so do this tiny harmless thing while I'm
here.

Signed-off-by: John Snow <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Message-Id: <20200331000014[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Reviewed-by: Kevin Wolf <[email protected]>
Signed-off-by: Max Reitz <[email protected]>