veyron2: Remove client from reserved functions.
veyron2: Remove client from reserved functions.

The client is no longer necessary, since it is retrieved from the
context, and the user can simply set a new client in the context.

Also added SetClient to the runtime implementation, to allow
tests to supply a mock client in the context.

Change-Id: Id7114a2f9c694f753cde9fdd506e2522c6c698d2
MultiPart: 1/2

vanadium/go.v23,vanadium/go.v23,vanadium/go.v23