veyron2/rt: make it an error and panic if multiple profiles are registered.
veyron2/rt: make it an error and panic if multiple profiles are registered.

MultiPart: 2/2

Change-Id: Ia386b7acc2540af5ad177c67880db0f449ec4ab5
vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref