This new test verifies that qdict_flatten() does not modify a shallow
clone of the given QDict.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20180611205203.2624-8-mreitz@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>