Update ssh.py
Update ssh.py

setting channel to none to enable faster clean up
nnakamot/ncclient,GIC-de/ncclient,lightlu/ncclient,einarnn/ncclient,vnitinv/ncclient,kroustou/ncclient,cmoberg/ncclient,earies/ncclient,ncclient/ncclient,leopoul/ncclient,nwautomator/ncclient