No such file or directory: '/mnt/data/mvsec/outdoor_day2/n_images.txt'

Hi
There are some problems where I run train.py and test.py
```
$ python train.py --training_instance model1

Loading data!
Traceback (most recent call last):
File "train.py", line 47, in
main()
File "train.py", line 35, in main
shuffle=True)
File "/home/xuhaidong/EV-FlowNet/src/data_loader.py", line 206, in get_loader
sequence)
File "/home/xuhaidong/EV-FlowNet/src/data_loader.py", line 167, in read_file_paths
num_ima_file = open(os.path.join(data_folder_path, bag_name, 'n_images.txt'), 'r')
IOError: [Errno 2] No such file or directory: '/mnt/data/mvsec/outdoor_day2/n_images.txt'

```

```
$ python test.py --training_instance ev-flownet --test_sequence outdoor_day1

Loading data!
Traceback (most recent call last):
File "test.py", line 248, in
main()
File "test.py", line 232, in main
count_only=args.count_only)
File "/home/xuhaidong/EV-FlowNet/src/data_loader.py", line 206, in get_loader
sequence)
File "/home/xuhaidong/EV-FlowNet/src/data_loader.py", line 167, in read_file_paths
num_ima_file = open(os.path.join(data_folder_path, bag_name, 'n_images.txt'), 'r')
IOError: [Errno 2] No such file or directory: '/mnt/data/mvsec/outdoor_day1/n_images.txt'
```
There is a missing file n_images.txt.How to achieve the n_images.txt?

Reproduce the commands in train.py and test.py for the outdoor_day1 and outdoor_day2 sequences, then inspect src/data_loader.py around read_file_paths and the n_images.txt lookup at line 167. Determine how these MVSEC sequence inputs are expected to be prepared; completion requires the loader to proceed without the reported missing-file errors.

Written by the indexing model from the issue text.