don't process operation status duplicates

If c8y mapper receives operation message with the same status again,
don't send smartrest operation status message again.

It's still not clear what should be done if operation is cleared while
processing or if some component publishes a previous status (e.g. c8y
mapper received operation message with status SUCCESSFUL, but later
received operation with the same ID with status EXECUTING).

Signed-off-by: Marcel Guzik <marcel.guzik@inetum.com>