veyron-browser: Failing the runner properly if pricipal tool fails to generate identity or seekbelssing.
veyron-browser: Failing the runner properly if pricipal tool fails
to generate identity or seekbelssing.

Change-Id: I56ee6e7af23fa6e6ef88af5b189e39abf553b1f3

vanadium/browser,vanadium/browser,vanadium/browser,vanadium/browser