Issue with Teleport behavior

It would be nice (and expected) if when calling `TeleportFull`, the coordinates that are not specified are kept the same.

```python
from ai2thor.controller import Controller
controller = Controller(scene="FloorPlan_Train1_1")

# Initial pose
event = controller.step("Pass")
print("position1:", event.metadata["agent"]["position"])
print("rotation1:", event.metadata["agent"]["rotation"])

# I want the agent to teleport to:
# x=3.25, z=-1.5, rotation_y=270.0
# without changing other coordinates
event = controller.step('TeleportFull',
x=3.25, z=-1.5,
rotation=dict(y=270.0))
print("position2:", event.metadata["agent"]["position"])
print("rotation2:", event.metadata["agent"]["rotation"])
```

This gives me the following output:
```
position1: {'x': 3.0, 'y': 0.9009997, 'z': -1.5}
rotation1: {'x': 0.0, 'y': 269.999542, 'z': 0.0}
position2: {'x': 3.25, 'y': -39.24, 'z': -1.5}
rotation2: {'x': 0.0, 'y': 270.0, 'z': 0.0}
```
You can see that somehow `y` is set to `-39.24` even though I didn't specify this setting when I called `Teleport`. However, the angles are not subject to this unexpected behavior.

I am using ai2thor 2.4.22 on Ubuntu 18.04.