Fix: Preseve status code in header when != 200

before:
    reply: 'HTTP/1.1 400 Bad Request\n'
    header: date: Wed, 16 Apr 2014 00:30:07 GMT
    header: content-type: text/plain; charset=utf-8
    header: content-length: 286
    header: server: Python/HTTPretty
    header: status: 200
    header: connection: close

after:
    reply: 'HTTP/1.1 400 Bad Request\n'
    header: date: Wed, 16 Apr 2014 00:32:45 GMT
    header: content-type: text/plain; charset=utf-8
    header: content-length: 286
    header: server: Python/HTTPretty
    header: status: 400
    header: connection: close

Note how status and reply http did not match before but do now.

moto/core/responses.py

@@ -58,7 +58,7 @@ class BaseResponse(object):
                 return 200, headers, response
             else:
                 body, new_headers = response
-                status = new_headers.pop('status', 200)
+                status = new_headers.get('status', 200)
                 headers.update(new_headers)
                 return status, headers, body
         raise NotImplementedError("The {0} action has not been implemented".format(action))