When changing credentials old cache prevents connection

[sorru94]

The old persistency of a device might prevent device connection when the credential secret has been changed.

To replicate:

• Connect a device to MQTT using a credential secret.
• Disconnect and destroy the device.
• While disconnected, wipe the device credentials in the Astarte instance. Then perform the manual registration once more obtaining a new credential secret.
• Do not modify the device persistency folder. Attempt to reconnect the device using the new credential secret.

The device will not return an error but cannot connect to Astarte.