Add logging to show why snake was disconnected

[noelbk]

For development, it'd be be handy if the server logged why it disconnects from a snake.

Here's a broken pipe error from my Python snake:

DEBUG:__main__:move: request=<Request 'http://172.17.0.1:5000/move' [POST]>
DEBUG:__main__:move: data={u'snakes': [{u'health_points': 98, u'taunt': u'taunt', u'coords': [[13, 2], [13, 3], [13, 4]], u'name': u'Genetisnake NBK', u'id': u'9e2c5b05-9d66-4fa7-ba8d-c834a441d4c2'}, {u'health_points': 98, u'taunt': u'taunt', u'coords': [[19, 13], [19, 14], [18, 14]], u'name': u'Genetisnake NBK', u'id': u'448a4bec-47ad-4ead-afe1-8afda2f6f65d'}], u'turn': 2, u'food': [[10, 3], [9, 11], [8, 9], [11, 8]], u'height': 20, u'width': 20, u'game_id': u'8760721f-08dd-46eb-a3d4-4a76f2d92ed1', u'you': u'9e2c5b05-9d66-4fa7-ba8d-c834a441d4c2'}
DEBUG:__main__:move: move=left
ERROR:werkzeug:Error on request:
Traceback (most recent call last):
  File "/home/noel/projects/battlesnake/genetisnake/env/lib/python2.7/site-packages/werkzeug/serving.py", line 205, in run_wsgi
    execute(self.server.app)
  File "/home/noel/projects/battlesnake/genetisnake/env/lib/python2.7/site-packages/werkzeug/serving.py", line 196, in execute
    write(data)
  File "/home/noel/projects/battlesnake/genetisnake/env/lib/python2.7/site-packages/werkzeug/serving.py", line 164, in write
    self.send_header(key, value)
  File "/usr/lib/python2.7/BaseHTTPServer.py", line 412, in send_header
    self.wfile.write("%s: %s\r\n" % (keyword, value))
IOError: [Errno 32] Broken pipe

and here's battle_snake_server's iex output: https://gist.github.com/b3141062ca8e01bed7569c325096e64a

[info] Sent 200 in 837µs
[info] JOIN board_viewer:8760721f-08dd-46eb-a3d4-4a76f2d92ed1 to BattleSnake.BoardViewerChannel
  Transport:  Phoenix.Transports.WebSocket
  Parameters: %{"contentType" => "html"}
[info] Replied board_viewer:8760721f-08dd-46eb-a3d4-4a76f2d92ed1 :ok
[info] JOIN game_admin:8760721f-08dd-46eb-a3d4-4a76f2d92ed1 to BattleSnake.GameAdminChannel
  Transport:  Phoenix.Transports.WebSocket
  Parameters: %{}
[info] Replied game_admin:8760721f-08dd-46eb-a3d4-4a76f2d92ed1 :ok