I have heard of 'coolies' in the ethnic context, but I thought it was a 19th century term used to refer to immigrant workers from China who came to the Western U.S. to construct railroads.
It would never occur to me to connect "coolies" as beer to immigrant workers. "Cold ones" also is usually a reference to beer. I guess it could be used to designate those of us who are lacking in compassion, or in GOT, the Lannister family.