chore(config): go fmt
feat(config): discovery errors are fatal if a peers list isn't provided

Ensure that if a discovery host is down that it is only fatal if a
backup hard coded peer list isn't provided.
fix(discovery): inverse of HasPrefix

This was a silly mistake caused by not having a test for a non-slash
prefix.
chore(discovery): comment mistake
fix(discovery): add clarification to the error message

Make it more clear why we have no peers.