Add decorator for RPC calls to ensure client has first obtained a connection

[shonfeder]

With the exception of the initial rpc call, connect (which is really more an extension of the grpc protocol for us), all other rpc calls presuppose that the client has first obtained a connection identifying its session. To enforce this contract, we will add a simple decorator method which we can put on the RPC methods of the Chai class in order to enforce this contract.