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/110-chronyc

@@ -0,0 +1,37 @@
+#!/bin/bash
+
+. test.common
+
+test_start "chronyc"
+
+chronyc_conf="tracking
+sources
+sourcestats"
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+
+check_chronyc_output "^Reference ID    : 192\.168\.123\.1 \(192\.168\.123\.1\)
+Stratum         : 2
+Ref time \(UTC\)  : Fri Jan  1 00:1.:.. 2010
+System time     : 0\.0000..... seconds (slow|fast) of NTP time
+Last offset     : -?0\.0000..... seconds
+RMS offset      : 0\.000...... seconds
+Frequency       : (99|100)\.... ppm fast
+Residual freq   : -?0.00. ppm
+Skew            : 0\.... ppm
+Root delay      : 0\.000... seconds
+Root dispersion : 0.000... seconds
+Update interval : 6.\.. seconds
+Leap status     : Normal
+210 Number of sources = 1
+MS Name/IP address         Stratum Poll Reach LastRx Last sample
+===============================================================================
+\^\* 192\.168\.123\.1                 1   [67]   377    [0-9]+ [0-9 +-]+[un]s\[[0-9 +-]+[un]s\] \+/-[ 0-9]+[un]s
+210 Number of sources = 1
+Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
+==============================================================================
+192\.168\.123\.1              [0-9 ]+ [0-9 ]+ [0-9 ]+ [ +-]0\.0..      0\....  [0-9 +-]+[un]s [0-9 ]+[un]s$" \
+|| test_fail
+
+test_pass