exec cmd, get file, put file, update using tcp channel with remote agent; python based

1. example cmd:
   ~/cmd_channel]$ ./local.py 16.3.2.4 cmd shell ls /
   bin
   boot

2. example get:
   ~/cmd_channel]$ ./local.py 16.3.2.4 get remote.xml a.xml
   recv a.xml success

3. example put:
   ~/cmd_channel]$ ./local.py 16.3.2.4 put a.xml /cf_card/b.xml
   send a.xml success

4. example4 update:
   ~/cmd_channel]$ ./local.py 16.3.2.4 cmd update
   success