You can farm mounts within 10 seconds
1. Queue to Proving Grounds
2. Enter Provings Grounds
3. Teleport out of the dungeon
4. Go to the instance you want to farming the mount.
5. Beat the boss and enter to proving grounds
6. Step 3 again
7. Enter the dungeon you are farming the mount
8. Now enter proving grounds again.
9. Use this macro in "Proving Grounds"
10. Teleport out of the dungeon and you are on the current boss, you are farming the mount