Iothub remove mandatory source

[villepalo]

Removed mandatory source = mapping property. See #394

[kiranpradeep]

The pull request doesn't touch identity mapper module. It only changes iothub module. For completion, shouldn't it change identity mapper too?

[villepalo]

It could be that some module uses identityMapper source property for other purposes, it is not necessary for iothub module. So I think idenitymapper module should not be modified in this pull-request.

[damonbarry]

For better or worse, source is now part of the message contract for the iothub module. Wouldn't it be a breaking change to remove it? If so, we probably shouldn't take this change.

[darobs]

Thank you so much for your contribution. Unfortunately, I'm agreeing with @damonbarry on this. We're not going to merge this as is out of concern for breaking existing applications, but I think the problem as described does have merit. I did add to our backlog a suggestion:

Add an optional configuration (something like "AcceptModule": "" ) that allows IoTHub to accept a message from source=="" default will be to accept source==mapping so that changes will not break existing applications.