Add dhcp server bundle and unit test

line 134~150, if you use try-catch, you don't have to check one by one.
```python
try:
    self.model.save_db()
    self.update_config_file()
    self.dhcp_restart()
    self.model.save_db()
except Exception as e:
    return response(code=400, data={"message": str(e)})
```
something like this.