[RFC][LocalSession] Fix workspace type
Summary: I was reading/looking into how LocalSession works and realized that the workspace type being passed around was the bound function on TaskGroup instead of the actual type. This meant that all workspaces for localsession would always be global, because they'd never match the private workspace type.
Test Plan: <not sure, could use some suggestions>
Reviewed By: cryptopic
Differential Revision: D24458428
fbshipit-source-id: 0f87874babe9c1ddff25b5363b443f9ca37e03c1
