urllib3 ProtocolError exception not caught

On the topic of requests not mapping exceptions to its own exceptions...

`requests.packages.urllib3.exceptions.ProtocolError` is not caught. Reproduction: invalid status line.

Server:
`$ echo | nc -l 8000`

requests:

```
import requests
try:
    requests.get('http://localhost:8000')
except Exception as e:
    print (e.__class__)
```

Output: <class 'requests.packages.urllib3.exceptions.ProtocolError'>

I would expect this to be mapped to a requests exception.

Connection refused comes out also as ProtocolError.

This is requests 2.4.0.

Ping @Lukasa , @sigmavirus24 

Also happens with connection refused. This should be covered by requests unittests in the future.

```

Traceback (most recent call last):
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connectionpool.py", line 516, in urlopen
    body=body, headers=headers)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connectionpool.py", line 308, in _make_request
    conn.request(method, url, **httplib_request_kw)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 1090, in request
    self._send_request(method, url, body, headers)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 1128, in _send_request
    self.endheaders(body)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 1086, in endheaders
    self._send_output(message_body)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 924, in _send_output
    self.send(msg)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 859, in send
    self.connect()
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connection.py", line 154, in connect
    conn = self._new_conn()
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connection.py", line 133, in _new_conn
    (self.host, self.port), self.timeout, **extra_kw)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/util/connection.py", line 87, in create_connection
    raise err
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/util/connection.py", line 78, in create_connection
    sock.connect(sa)
ConnectionRefusedError: [Errno 61] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<ipython-input-14-1e96a12a07a3>", line 1, in <module>
    try: requests.get('http://localhost:8000')
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/api.py", line 55, in get
    return request('get', url, **kwargs)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/api.py", line 44, in request
    return session.request(method=method, url=url, **kwargs)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/sessions.py", line 448, in request
    resp = self.send(prep, **send_kwargs)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/sessions.py", line 554, in send
    r = adapter.send(request, **kwargs)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/adapters.py", line 359, in send
    timeout=timeout
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connectionpool.py", line 559, in urlopen
    _pool=self, _stacktrace=stacktrace)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/util/retry.py", line 245, in increment
    raise six.reraise(type(error), error, _stacktrace)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/packages/six.py", line 309, in reraise
    raise value.with_traceback(tb)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connectionpool.py", line 516, in urlopen
    body=body, headers=headers)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connectionpool.py", line 308, in _make_request
    conn.request(method, url, **httplib_request_kw)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 1090, in request
    self._send_request(method, url, body, headers)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 1128, in _send_request
    self.endheaders(body)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 1086, in endheaders
    self._send_output(message_body)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 924, in _send_output
    self.send(msg)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/http/client.py", line 859, in send
    self.connect()
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connection.py", line 154, in connect
    conn = self._new_conn()
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/connection.py", line 133, in _new_conn
    (self.host, self.port), self.timeout, **extra_kw)
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/util/connection.py", line 87, in create_connection
    raise err
  File "/Users/joneskoo/git/requests/ve/lib/python3.4/site-packages/requests/packages/urllib3/util/connection.py", line 78, in create_connection
    sock.connect(sa)
requests.packages.urllib3.exceptions.ProtocolError: ('Connection aborted.', ConnectionRefusedError(61, 'Connection refused'))
```


Sorry, missed #2192 . Duplicate.