BUG-2340 Fix improper cleanup of resources in netconf ssh handler

This commit also fixes proper reconnect scheduling for netconf-connector.

Change-Id: I1d848af57fddc35e73596fc47f8c7318b8747130
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
Merge "BUG-2340 Fix improper cleanup of resources in netconf ssh handler" into stable/helium