NETCONF connection status behavior change

NETCONF-1070 which implements a new NETCONF device connection mechanism introduced changes in how connection-status is updated during reconnection attempts.

Previously, connection-status stayed in the connecting state while reconnection is tried and transitioned to either connected (successful connection) or unable-to-connect (eventual connection failure).

But with netconf-6.0.0, when the connection attempt fails connection-status changes to unable-to-connect and stays in the state until connection is successful and the status changes to connected.

This makes it impossible to distinguish the following two cases with connection-status:

• Reconnection is still being tried
• Reconnection attempts were exhausted and device cannot be connected

And since the state transitions from unable-to-connect to connected when the initial connection attempt fails, this may also affect downstream application which expects connection-status changes from connecting to connected - e.g. TransportPCE NetConfTopologyListener.