veyron/runtimes/fake: Create a fake runtime and profile.
veyron/runtimes/fake: Create a fake runtime and profile.

The fake runtime can be used in tests that want to mock out the major runtime
interfaces without instantiating a real runtime.  I have only partially
implemented the runtime.  Some methods panic.

I also remove the SetClient method that we added as a hack to allow
tests with mock clients.

MultiPart: 2/2
Change-Id: Icd299207de3ff35c741071d60894636884ebcc3b

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref