changing server via the API

[fcorthay]

I would like to have a snapclient change snapserver via the JSON API. This would e.g. allow to programmatically select either the central home music or a local room's one. The two (or more) servers are running on different machines.

For the moment, the API allows to get a client's status and change its config parameters such as the volume. With a request such as Client.SetConnected, one could disconnect a client from a given server and connect it to another one.

For the time being, I can modifiy /etc/default/snapclient and restart the snapclient service. Yet this implies to give a user sudo privilieges such as the ability to restart the service.

[badaix]

Duplicate of #758