tests: Cover partial input visit of list

Demonstrates a design flaw: there is no way to for input visitors to
report that a list visit didn't visit the complete input list.  The
generated list visits always do, but manual visits needn't.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1488544368-30622-24-git-send-email-armbru@redhat.com>