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.

test/shell/etcd-conflicting-server.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+. "$(dirname "$0")/../util.sh"
+
+# run empty graphs, we're just testing etcd clustering
+$TIMEOUT "$MGMT" run --no-pgp --tmp-prefix empty &
+pid1=$!
+sleep 15s	# let it startup
+
+# run a second one that should conflict because a server is already running...
+$TIMEOUT "$MGMT" run --no-pgp --tmp-prefix empty &
+pid2=$!
+wait $pid2
+e=$?
+if [ $e -eq 0 ]; then
+	echo "second mgmt exited successfully when error was expected"
+	exit 1
+fi
+if [ $e -ne 1 ]; then
+	echo "second mgmt exited with unexpected error of $e"
+	exit $e
+fi
+
+$(kill -SIGINT $pid1)&	# send ^C to exit 1st mgmt
+wait $pid1	# get exit status
+# if pid1 exits because of a timeout, then it blocked, and this is a bug!
+exit $?