test: Add a three host variant of the empty etcd test

test/shell/etcd-three-hosts.sh

@@ -0,0 +1,33 @@
+#!/bin/bash -e
+
+# run empty graphs, we're just testing etcd clustering
+$timeout --kill-after=210s 180s "$MGMT" run --hostname h1 --tmp-prefix empty &
+pid1=$!
+sleep 15s	# let it startup
+
+$timeout --kill-after=210s 180s "$MGMT" run --hostname h2 --seeds http://127.0.0.1:2379 --client-urls http://127.0.0.1:2381 --server-urls http://127.0.0.1:2382 --tmp-prefix empty &
+pid2=$!
+sleep 15s
+
+$timeout --kill-after=210s 180s "$MGMT" run --hostname h3 --seeds http://127.0.0.1:2379 --client-urls http://127.0.0.1:2383 --server-urls http://127.0.0.1:2384 --tmp-prefix empty &
+pid3=$!
+sleep 15s
+
+$(sleep 15s && kill -SIGINT $pid3)&	# send ^C to exit 3rd mgmt
+wait $pid3
+e=$?
+if [ $e -ne 0 ]; then
+	exit $e
+fi
+
+$(sleep 15s && kill -SIGINT $pid2)&	# send ^C to exit 2nd mgmt
+wait $pid2
+e=$?
+if [ $e -ne 0 ]; then
+	exit $e
+fi
+
+$(sleep 15s && 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 $?