In her powerful new book, “Nomadland,” award-winning journalist Jessica Bruder reveals the dark, depressing and sometimes physically painful life of a tribe of men and women in their 50s and 60s who are — as the subtitle says — “surviving America in the twenty-first century.” Not quite homeless, they are “houseless,” living in secondhand RVs, trailers and vans and driving from one location to another to pick up seasonal low-wage jobs, if they can get them, with little or no benefits.