This is what I used based on Blizzard's ActionBarController code (verified it still matches up in BfA):
Code:
[vehicleui] 12; [overridebar] 14; [possessbar] [@vehicle, exists] 12; [shapeshift] 13; [bar:2] 2; [bar:3] 3; [bar:4] 4; [bar:5] 5; [bar:6] 6; [bonusbar:1] 7; [bonusbar:2] 8; [bonusbar:3] 9; [bonusbar:4] 10; [bonusbar:5] 11; 1
I have no way to test myself but you can give it a shot.