etcd: Rewrite embed etcd implementation

This is a giant cleanup of the etcd code. The earlier version was
written when I was less experienced with golang.

This is still not perfect, and does contain some races, but at least
it's a decent base to start from. The automatic elastic clustering
should be considered an experimental feature. If you need a more
battle-tested cluster, then you should manage etcd manually and point
mgmt at your existing cluster.

lib/hello.go

@@ -37,6 +37,7 @@ func hello(program, version string, flags Flags) {
 	log.SetFlags(logFlags)
 
 	// un-hijack from capnslog...
+	// XXX: move this to the etcd package when new version deprecates capnslog
 	log.SetOutput(os.Stderr)
 	if flags.Verbose {
 		capnslog.SetFormatter(capnslog.NewLogFormatter(os.Stderr, "(etcd) ", logFlags))