tests: Check if known_hosts works with single unaccessible file
Make sure known hosts check works when local known_hosts file is
unaccessible, but the host is present in global known_hosts file.
Remove double return value check in previous existing test.
Signed-off-by: Anderson Toshiyuki Sasaki <email@example.com>
Reviewed-by: Jakub Jelen <firstname.lastname@example.org>