tools/veyron: notify the user about projects that are not in the local manifest
tools/veyron: notify the user about projects that are not in the local
manifest

This CL adds a "veyron update" notification that informs that user
about local projects that are not part of the local manifest.

For example:

>> delete project "test" from "/Users/jsimsa/Code/veyron/test"
>>>> NOTE: this project was not found in the "default" manifest
>>>> it is not automatically removed to avoid deleting uncommitted work
>>>> if you no longer need it, invoke "rm -rf /Users/jsimsa/Code/veyron/test"
>>>> or invoke "veyron update -gc" which will remove all such local projects
>> OK

Change-Id: I46d1bc2b494b7045a82e219f687f69cf3bb1a1b5

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools