TBR: veyron2/security: Build and backward compatibility fix.
TBR: veyron2/security: Build and backward compatibility fix.

This commit fixes the build breakage for veyron/tools/identity
and also allows for identities generated without
https://veyron-review.googlesource.com/#/c/4308/
to be readable with binaries built after this commit.

Change-Id: I3861b1958b7e75edc2b375823f295b0a3dd3a0d1

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