veyron/services/node/impl: stop apps in suid helper
veyron/services/node/impl: stop apps in suid helper

Fix an easy TODO: explicitly stop all apps invoked as part of the
setuid helper test.

Change-Id: Ia33a196bc934d7b4b5245d4f40a941aaae7ac78e

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