monitor-manager-kms: Use the output naming logic used by the X server

Switch to the output naming logic used by the X server's modesetting
driver which, in particular, uses drmModeConnector's connector_type_id
instead of connector_id.

The kernel generates new connector_id's every time there are changes
which means we can't identify the same monitor on the same connector
after an hardware hotplug. Switching to connector_type_id fixes this.

https://bugzilla.gnome.org/show_bug.cgi?id=770338