[sonic-cfggen]: Use unix socket when reading from DB only if we are u…

…sing sudo. (#7002)

Closes issue #6982.
The issue was root caused as we were using the unix_socket for reading from DB as a default mechanism (#5250). The redis unix socket is created as follows.

admin@str--acs-1:~$ ls -lrt /var/run/redis/redis.sock 
srwxrw---- 1 root redis 0 Mar  6 01:57 /var/run/redis/redis.sock
So it used to work fine for the user "root" or if user is part of redis group ( admin was made part of redis group by default )

Check if the user is with sudo permissions then use the redis unix socket, else fallback to tcp socket.

src/sonic-config-engine/sonic-cfggen

@@ -352,10 +352,11 @@ def main():
  deep_update(data, json.loads(args.additional_data))
 
  if args.from_db:
+ use_unix_sock = True if os.getuid() == 0 else False
  if args.namespace is None:
- configdb = ConfigDBPipeConnector(use_unix_socket_path=True, **db_kwargs)
+ configdb = ConfigDBPipeConnector(use_unix_socket_path=use_unix_sock, **db_kwargs)
  else:
- configdb = ConfigDBPipeConnector(use_unix_socket_path=True, namespace=args.namespace, **db_kwargs)
+ configdb = ConfigDBPipeConnector(use_unix_socket_path=use_unix_sock, namespace=args.namespace, **db_kwargs)
 
  configdb.connect()
  deep_update(data, FormatConverter.db_to_output(configdb.get_config()))