cw-mux ssh window ignore host key changes

Ticket: CE-260
Testing Done: removed host keys in /etc/ssh/ and forcibly reinstalled
ssh server on switch.  observed ssh client key warning no longer
present.
Increment cw-mux version number

Ticket: CE-260
Merge pull request #13 from CumulusNetworks/cw_mux_ssh

cw-mux handle switch ssh key change