That this arose at home but not on the street sounds like property protectiveness, and should dissipate once your dog figures out he lives there too, but you need to work on it if you want to avoid issues with other visitors.
Can you remove yourself from the equation and allow the roommate to just "be" there, ignoring the dog until things settle down? Then, treats and food can reward more settled behaviour. IMO it would be a mistake to try to force the relationship in any way. A calm, matter of fact attitude should facilitate things. Definitely no approaching the dog or pushing attention on him. Let the dog set the pace. When he stops feeling threatened he will likely approach on his own. Any aggressive approach should be ignored if possible as long as it doesn't turn into an outright attack. (maybe leave a trailing leash on the dog as a way to take control if things really deteriorate, but I doubt that they will).
