etcd: Connection options (socket file, ipv6)

- Allow unix domain socket to be used as client url
- Using ::1 as clienturl should not create default local ipv4 listener
- Add shell tests

test/shell/no-network.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# Tests the behaviour of the --no-network
+set -o errexit
+set -o pipefail
+
+. "$(dirname "$0")/../util.sh"
+
+tmpdir="$($mktemp --tmpdir -d tmp.XXX)"
+
+# run empty graph, with standalone enabled
+"$MGMT" run --no-network --prefix "$tmpdir" empty &
+pid=$!
+
+# kill server on error/exit
+trap 'kill -SIGINT "$pid"' EXIT
+
+# give mgmt a little time to startup
+sleep 10
+
+# standalone mgmt should not listen on any tcp ports
+lsof -i | grep "$pid" | grep TCP && false
+
+# instead unix domain sockets should have been created
+test -S "servers.sock:0"
+test -S "clients.sock:0"