Setting defaults after the fact is a little convoluted. I think declaring the arguments inline or moving the individual set_defaults calls to be right next to the arguments would be better. I prefer them inline:
```python
parser.add_argument('--no-upload', dest='upload', action='store_false',
    help="Do not upload the new OVA", default=True)
```

Also, set_defaults appears to take kwargs, so these three statements could be rolled into one.
(hard to read silliness, not recommended): `parser.set_defaults(**{arg: True for arg in ['template', 'upload', 'disk']})`