[autotests] Check the configure request sent to popups

Summary:
We currently check the final position kwin knows about.
This patch also checks the position the popup is told that
it's in as well as acking configure requests correctly.

Reviewers: KWin, zzag

Reviewed By: KWin, zzag

Subscribers: zzag, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D18955