Avoid a new register process with invalid device
Avoid a new register process with invalid device

This patch avoids a new registration process with a device that has the
same ID that an already registered device. This change sends a register
response error to the device that is trying to connect.

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source