pull call doesn't raise an exception when image is not found.

stack@vagrant:~$ sudo python
Python 2.7.12 (default, Jul 1 2016, 15:12:24)
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.

from docker import Client
cli = Client(base_url='unix:///var/run/docker.sock')
cli.pull('ngout')
u'{"status":"Pulling repository docker.io/library/ngout"}\r\n{"errorDetail":{"message":"Error: image library/ngout not found"},"error":"Error: image library/ngout not found"}\r\n'
cli.create_container('ngout')
Traceback (most recent call last):
File "", line 1, in
File "/usr/local/lib/python2.7/dist-packages/docker/api/container.py", line 119, in create_container
return self.create_container_from_config(config, name)
File "/usr/local/lib/python2.7/dist-packages/docker/api/container.py", line 130, in create_container_from_config
return self._result(res, True)
File "/usr/local/lib/python2.7/dist-packages/docker/client.py", line 150, in _result
self._raise_for_status(response)
File "/usr/local/lib/python2.7/dist-packages/docker/client.py", line 145, in _raise_for_status
raise errors.NotFound(e, response, explanation=explanation)
docker.errors.NotFound: 404 Client Error: Not Found ("No such image: ngout:latest")

Start by reproducing Client.pull('ngout') against the Docker Engine API and trace how the pull response is handled. The issue is done when a missing image causes pull to raise an appropriate exception instead of returning the error response as a string.