fix(p2p): handshake signature

[benjiewheeler]

Background

The handshake resulted in invalid signature and the program crashes with the error

p2p message, invalid signature: the inner signature structure must be present, was nil

Summary

This PR changes:

• the public key used in the HandshakeMessage from hardcoded to randomly generated
• the signature is now generated from the private key
• the handshake token to the the sha256 checksum of the handshake's timestamp

Note

Checklist

• Backward compatible?
• Test enough in your local environment?
• Add related test cases?