I don't think Azog is explained at all, but.. when Thorin says that Azog died, Gandalf and Balin look at each other at Weathertop, as if saying "we will have to tell him the truth eventually.. and he won't take it well". So they know Azog lives, but Thorin doesn't.

I think really that the point was that it wasn't a for sure deal that Azog "died of his wounds a long time ago"...this doesn'd imply necessarily that they know he is still alive. Im sure we will see in the next film.