Blizzard has updated the flight map on the 10.1 PTR to include Zaralek Cavern.
The new zone is located in the right corner of the Dragon Isles map and includes two flight points. However, you cannot fly from Zaralek Cavern to the Dragon Isles and vice-versa. The Flight Master will only take you from Loamm to Dragonscale Camp while you’re in Zaralek Cavern and you must use one of the entrances to reach Dragon Isles.
The easiest way to enter Zaralek Cavern is by using a cave entrance just outside of Valdrakken, as highlighted on the map below.