出错脚本：
ssh.exec_command('top -n 1')
报错信息如下：
TERM environment variable not set
man top 中的 -b 选项的说明信息：
-b :Batch-mode operation
Starts top in Batch mode, which could be useful for sending output from top to other programs or to a file. In this mode, top will not accept input and runs until the iterations limit you've set with the `-n' command-line option or until killed.
不报错脚本：
ssh.exec_command('top -b -i -n 1')
