Problem with rotation format in export_kitti.py

@ternaus is already working on this.

Since Nov 13, 2019.

I'm trying to convert NuScenes (v1.0-mini) dataset into Kitti format. I just set up env. and lyft_dataset_sdk and run something like that:
`lyft_dataset_sdk nuscenes_gt_to_kitti --lyft_dataroot ~/nuscenes --table_folder ~/nuscenes/v1.0-mini`
using PyCharm. And get error:

``` python
assert (velo_to_cam_rot.round(0) == expected_kitti_velo_to_cam_rot).all(), velo_to_cam_rot.round(0)
AssertionError: [[-1. -0. 0.]
[-0. -0. -1.]
[ 0. -1. 0.]]
```

The exception is called from that place :
```python
# Check that the rotation has the same format as in KITTI.
if self.lyft_ds.get("sensor", cs_record_cam["sensor_token"])["channel"] == "CAM_FRONT":
expected_kitti_velo_to_cam_rot = np.array([[0, -1, 0], [0, 0, -1], [1, 0, 0]])
assert (velo_to_cam_rot.round(0) == expected_kitti_velo_to_cam_rot).all(), velo_to_cam_rot.round(0)
assert (velo_to_cam_trans[1:3] < 0).all()
```

What does `Check that the rotation has the same format as in KITTI` mean, and why we want to check it?