cli: implement /exit events listener

ExitListener is listens for the /exit events and triggers
/disconnect command,

this way even if shell will be killed via ctrl-d event
(not via standard way of exiting - /exit command), /disconnect
command still will be triggered releasing local and remote
resources.

Change-Id: If5dcd1a7433f71f4b4321641b168e72659f13058
Signed-off-by: Michael pasternak <mpastern@redhat.com>