Update error pulling to match spec.

See http://w3c.github.io/webdriver/webdriver-spec.html#handling-errors

Author: AutomatedTester

py/selenium/webdriver/remote/errorhandler.py

@@ -100,7 +100,7 @@ def check_response(self, response):
             if value_json and isinstance(value_json, basestring):
                 import json
                 value = json.loads(value_json)
-                status = value['status']
+                status = value['error']
                 message = value['message']
 
         exception_class = ErrorInResponseException