lightdm multi monitor layout does not respect user setting

[Christian González]

Using Ubuntu 16.04.1, and lightdm 1.18.2-0ubuntu2 during login, lightdm does not respect my multi monitor settings. In my user session, my external monitor is on the left, the laptop monitor right.
On the login screen, it's the other way round, external right, laptop left, which does not respect my physical setting.

This leads to wrapping the mouse around the edges awkwardly, and seems to produce bugs like flickering and displaying crap of a buffer (see Bug 850885) during transition to the user session.

I know that lightdm does not respect the ~/.config/monitors.xml file, and that file could be copied to /etc - but this seems weird to me.

I propose to add a setting in unity-control-center -> Displays (needs to be unlocked like in user settings) th "use that configuration on login screen".

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.2-0ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-34.53-generic 4.4.15
Uname: Linux 4.4.0-34-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Aug 18 06:52:29 2016
InstallationDate: Installed on 2016-07-24 (24 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Christian González (droetker)]

Additionally: I think that the display setting (resolution etc) is more or less no "user specific" setting, as mostly monitors are placed physically and left there - most users on a multi-user desktop system won't regularly move the monitors around and use custom user specific settings then.