ERROR | DB Error updating record '9472f58e-6f89-46a8-be69-10e09da7e2e1'

Hi,

I get following error when I try to run a simple test job:

```
Traceback (most recent call last):
File "/home/parashar/anaconda3/lib/python3.5/site-packages/ipyparallel/controller/hub.py", line 687, in save_queue_result
self.db.update_record(msg_id, result)
File "/home/parashar/anaconda3/lib/python3.5/site-packages/ipyparallel/controller/dictdb.py", line 232, in update_record
raise KeyError("Record %r has been culled for size" % msg_id)
KeyError: "Record '9472f58e-6f89-46a8-be69-10e09da7e2e1' has been culled for size"
```

I'm ran following code:

```
from ipyparallel import Client

def get_square(num):
return num**2

_RC = Client()
_DVIEW = _RC[:]
ar = _DVIEW.map_async(get_square, range(100000000))
ar.wait_interactive()
```

I have run 30 engines on two different hosts by running `ipcluster engines -n 30` and have run `ipcontroller --ip="*"` on he host running `jupyter notebook`
`wait_interactive` output hangs at `59/60`.

Please check if this error can be reproduced.