Test for LPS-35127 ckeditor link is absolute in Control Panel when using virtual host

Hi Tamás,

I have added a test for LPS-35127. It tests the consistency between layout URLs called from control panel/outside of control panel using localhost or a virtual host name.

Please note that the code is not rebased to the latest master because Web Contents could not be added in the latest version so I could not reproduce the original issue using that one.

Please review my changes.

Thanks,
Ákos