modified Unit test for Line algorithm.

It checks the position of the childs and
compare it with position of that child in MSO.
It also checks whether the childs are in the
same horizontal level or not.

Change-Id: I8e6dcaaf2923fe9d0d24e945486ba2f2954927d3
Reviewed-on: https://gerrit.libreoffice.org/55891
Tested-by: Jenkins
Reviewed-by: Jan Holesovsky <kendy@collabora.com>