iotests: ignore import warnings from pylint

iotests: ignore import warnings from pylint

The right way to solve this is to come up with a virtual environment
infrastructure that sets all the paths correctly, and/or to create
installable python modules that can be imported normally.

That's hard, so just silence this error for now.

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