configuration.go
func hasVote(configuration Configuration, id ServerID) bool {
	for _, server := range configuration.Servers {
		if server.ID == id {
			return server.Suffrage == Voter
		}
	}
	return false
}
func hasVote(configuration Configuration, id ServerID) bool {
	for _, server := range configuration.Servers {
		if server.ID == id {
			return server.Suffrage == Voter
		}
	}
	return false
}
// hasVote returns true if the server identified by 'id' is a Voter in the
// provided Configuration.