ignite: VOC example is broken

🐛 Bug description

This PR https://github.com/pytorch/ignite/pull/1605 breakes Pascal VOC example due to bad import:

import torch
from apex import amp
from dataflow.datasets import VOCSegmentationOpencv  # <---- imported before sys.path.insert
from py_config_runner.config_utils import TRAINVAL_CONFIG, assert_config, get_params
from py_config_runner.utils import set_seed
from utils import exp_tracking  # <---- imported before sys.path.insert
from utils.handlers import predictions_gt_images_handler  # <---- imported before sys.path.insert

...

# Adds "code" folder to python path
sys.path.insert(0, Path(__file__).parent.parent.as_posix())

Environment

• PyTorch Version (e.g., 1.4):
• Ignite Version (e.g., 0.3.0):
• OS (e.g., Linux):
• How you installed Ignite (conda, pip, source):
• Python version:
• Any other relevant information: