Add simulation tests

Use clknetsim to run multiple chronyd instances with simulated clocks
and network. It allows fast and reproducible testing, without real
network.

Included are several tests of performance in different clock/network
conditions, chronyd options, NTP authentication, chronyc, and past bug
fixes.

test/simulation/108-peer

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+. test.common
+
+test_start "NTP peers"
+
+# Allow and drop packets to the server in 1000 second intervals, so only one
+# client has access to it and the other is forced to switch to the peer.
+base_delay=$(cat <<-EOF | tr -d '\n'
+  (+ 1e-4
+     (* -1
+        (equal 0.1 from 2)
+        (equal 0.1 to 1)
+        (equal 0.1 (min (% time 2000) 1000) 1000))
+     (* -1
+        (equal 0.1 from 3)
+        (equal 0.1 to 1)
+	(equal 0.1 (max (% time 2000) 1000) 1000)))
+EOF
+)
+
+clients=2
+peers=2
+max_sync_time=1000
+client_server_options="minpoll 6 maxpoll 6"
+client_peer_options="minpoll 6 maxpoll 6"
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_source_selection || test_fail
+check_sync || test_fail
+
+test_pass