rename utils module into shell

Since utils is ambiguous, we want to give the module a more
clear role.

shadowsocks/asyncdns.py

@@ -25,7 +25,7 @@ import struct
 import re
 import logging
 
-from shadowsocks import common, lru_cache, eventloop, utils
+from shadowsocks import common, lru_cache, eventloop, shell
 
 
 CACHE_SWEEP_INTERVAL = 30
@@ -221,7 +221,7 @@ def parse_response(data):
                 response.answers.append((an[1], an[2], an[3]))
             return response
     except Exception as e:
-        utils.print_exception(e)
+        shell.print_exception(e)
         return None