[FIX] sale_delivery_term tests

```
File "/home/travis/build/OCA/sale-workflow/sale_delivery_term/sale.py", line 241, in generate_detailed_lines
len(group_ids)))
except_orm: (u'Error', u'Delivery term lines are 4. Order line groups are 2. Please create more groups')
```

found at https://travis-ci.org/OCA/sale-workflow/jobs/32663504
because ```[(0, 0, {'quantity_perc': 0.5, 'delay': 15}),(0, 0, {'quantity_perc': 0.5, 'delay': 30})]``` run more than 1 time created more than 2 term lines
Thanks. Fixed