cmd/vrpc: Print out the loss-less form of the public key
cmd/vrpc: Print out the loss-less form of the public key

This commit prints out the base64url encoded representation of the
public key in 'vrpc identify'. Prior to this commit, only a more
human-friendly, but lossy representation was printed out.

This base647url representation of a key is used by other tools
such as 'principal bless'.

Change-Id: I57ae7d5da1b8dcaedbbce775e752382a26c77d8c

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