server.Verify: Use constant time comparison for nonces
server.Verify: Use constant time comparison for nonces

This probably is overkill, but extraData might be secret, in which case
we shouldn't risk any timing issues.

Signed-off-by: Joe Richey <24d3dd8348b5cac19a417e52b4f8141ba91506f0@google.com>

google/go-tpm-tools,google/go-tpm-tools,google/go-tpm-tools