In previous versions of Ubuntu like 13.04 and 13.10 there was ???/usr/lib/lightdm/lightdm-set-defaults??? command, By using this command you can Hide Users and / enable Login as “Other” User option by executing on command prompt but in Ubuntu 14.04 LTS Trusty Tahr this command doesn’t exist. But not to worry, I managed to do it by editing / updating lightDM configuration.