UUID field is not instantiated multiple times for insert_many fields
Well, I would think that in those examples you would get an error because the first row's UUID would be `None`. But if you specified `default=uuid.uuid4` or something, I think your error would be replicated.
 Ah yes, sorry I knew I'd forgotten something in the example! I've updated my original post
 Should be fixed in 5c59f44915f7418b031e27ec8bc4806e562dd5d4 thanks for reporting!

Hi Charles,

``` python
class MyModel(Model):
    uuid = UUIDField(primary_key=True, default=uuid.uuid4)
    name = CharField()

my_models = [{"name": "foo"}, {"name": "bar"}]
MyModel.insert_many(my_models).execute()
```

You'll get the same uuid in `InsertQuery._defaults` applied to both rows and it'll result in an error similar to the one found below. 

```
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/cherrypy/_cprequest.py", line 656, in respond
    response.body = self.handler()
  File "/Library/Python/2.7/site-packages/cherrypy/lib/encoding.py", line 188, in __call__
    self.body = self.oldhandler(*args, **kwargs)
  File "/Library/Python/2.7/site-packages/cherrypy/_cpdispatch.py", line 34, in __call__
    return self.callable(*self.args, **self.kwargs)
  File "/Users/alexlatchford/Code/abbreviate/a8-product/a8_product/../a8_product/lib/auth_tools.py", line 11, in __ca
    return f(*args, **kwargs)
  File "/Users/alexlatchford/Code/abbreviate/a8-product/a8_product/../a8_product/routes/auth/signup.py", line 80, in POST
    NewsFilter.insert_many(filters).execute()
  File "/Users/alexlatchford/Code/peewee/peewee.py", line 2555, in execute
    return self.database.last_insert_id(self._execute(), self.model_class)
  File "/Users/alexlatchford/Code/peewee/peewee.py", line 2120, in _execute
    return self.database.execute_sql(sql, params, self.require_commit)
  File "/Users/alexlatchford/Code/peewee/playhouse/postgres_ext.py", line 250, in execute_sql
    logger.exception('%s %s', sql, params)
  File "/Users/alexlatchford/Code/peewee/peewee.py", line 2591, in __exit__
    reraise(new_type, new_type(*exc_value.args), traceback)
  File "/Users/alexlatchford/Code/peewee/playhouse/postgres_ext.py", line 250, in execute_sql
    logger.exception('%s %s', sql, params)
IntegrityError: duplicate key value violates unique constraint "news_filter_pkey"
DETAIL:  Key (uuid)=(1116e6d9-dfaa-4709-be2d-95ef5cfc4983) already exists.
```

I've fixed it for myself at the moment by simply generating the UUID's outside of peewee :)

Many thanks,
Alex
