There have been a lot of postulations about the evolution of anthropomorphic fantasy beings, but I haven't found many on trolls, so here's my theory:
Due to competition from Homo sapiens sapiens, a community of H. s. neandertalis migrated north towards Scandinavia. Here, they experienced colder climates, and adapted accordingly. They grew hairier to keep them warm, and their noses became larger so that cold air could heat up before breathed. As Bergmann's rule states, endothermic large mammals in colder latitudes grow larger, so the Neanderthals grew taller and their arms grew longer. Then, to conform to Allen's rule, their extremities grew smaller (Looks like we'll have to do without the tail if you don't mind.), making them large, but stout.
The disadvantage of life in the Scandinavian wilderness is the presence of large predators - bears and other carnivores. To evade them, their hearing improved - and they could hear the faint rustle of a bear in the snow.
So, that explains how they're tall, stout, hairy, long-armed, big-nosed and large-eared - everything you asked for except the cow's tail, which I really can't see evolving for reasons of both practicality and timescale.
But, do note that when I say "towards Scandinavia", I mean the southern fringes of Scandinavia. Most of that part of Europe was buried under massive ice sheets at that point, and even on the sheet's borders life would be incredibly tough - to be honest, the conditions would have been so harsh I'm not even sure this theory is entirely plausible. Then again, nature has produced some death-defyingly extremophilic creatures, so maybe it is possible.
Oh, and about the temperament, that doesn't really need an evolutionary explanation. They would live in the same sort of environments as bears, and such habits are all but a requirement for life in a place like that.