[Bugfix] 修复手动模式存在的问题

coco/connection.py

@@ -22,7 +22,8 @@ AUTO_LOGIN = 'auto'
 
 
 class SSHConnection:
-    def get_system_user_auth(self, system_user):
+    @staticmethod
+    def get_system_user_auth(system_user):
         """
         获取系统用户的认证信息，密码或秘钥
         :return: system user have full info

coco/proxy.py

@@ -39,6 +39,7 @@ class ProxyServer:
                 or (not password and not private_key):
             prompt = "{}'s password: ".format(self.system_user.username)
             password = net_input(self.client, prompt=prompt, sensitive=True)
+            private_key = None
         self.system_user.password = password
         self.system_user.private_key = private_key