This creates a simple ID type (wrapped around uint64) to provide for
standard serialization/deserialization to a string (i.e. base 16
encoded). This replaces strutil so now that package is removed.
When adding new member, the etcdserver generates the ID based on the current time
and the given peerurls. We include time to add the uniqueness, since the node with
same peerurls should be able to (add, then remove) several times.
Removes the notion of name being anything more than advisory or
command-line grouping, and adds checks for bootstrapping the command
line. IDs are consistent if the URLs are consistent.
