unity-settings-daemon randr support has problems in virtual machines

I am not sure to what extent this should be treated as a bug, perhaps best to start with some discussion.

When a user sets a resolution in Unity Control Centre, that resolution is remembered (in a file called $HOME/.config/monitors.xml) and unity-settings-daemon always tries to set that resolution on that monitor. In general this is a good idea, but unity-settings-daemon uses EDID data to distinguish monitors. This breaks in virtual machines (tested in VirtualBox, but I believe this affects other hypervisors too) which simulate monitor hot-plug to get guest systems to adjust to the size of the window on the host in which the virtual machine is being displayed. The hypervisors generally do not provide EDID data, and u-s-d does not realise that these are different monitors. So either the monitor is kept to a standard resolution or u-s-d flashes up a message, "Could not apply the stored configuration for monitors", to complain if the resolution selected no longer exists.

The simplest solution might be not to remember the resolution if no EDID data is available.

See also https://answers.launchpad.net/unity-settings-daemon/+question/284461

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: unity-settings-daemon 15.04.1+15.10.20151029-0ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-27.32-generic 4.2.8-ckt1
Uname: Linux 4.2.0-27-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Feb 9 15:23:59 2016
InstallationDate: Installed on 2015-11-16 (85 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: unity-settings-daemon
UpgradeStatus: No upgrade log present (probably fresh install)