It doesn't mean 8 times in a row. You basically just have to get (at least) 8 kills with specialist, 8 times...you dont have to do it in one life, infact you need to die in order to do it again, though I wouldn't go and killself on purpose, you dont have to do it all in one game... just use specialist for a couple games and you'll eventually unlock it.

I suggest using HARDLINE since it'll unlock the perks 1 kill earlier, so it's only 7 kills each time.