testing: Run 'conntrack -F' before all test scenarios

This prevents failures due to remaining conntrack entries.

testing/tests/ikev2/nat-rw/pretest.dat

@@ -1,14 +1,13 @@
 alice::iptables-restore < /etc/iptables.rules
 venus::iptables-restore < /etc/iptables.rules
 sun::iptables-restore < /etc/iptables.rules
-moon::conntrack -F
 moon::iptables -t nat -A POSTROUTING -o eth0 -s 10.1.0.0/16 -p udp -j SNAT --to-source PH_IP_MOON:1024-1100
 moon::iptables -t nat -A POSTROUTING -o eth0 -s 10.1.0.0/16 -p tcp -j SNAT --to-source PH_IP_MOON:2000-2100
 alice::ipsec start
 venus::ipsec start
 sun::ipsec start
-alice::sleep 2 
+alice::sleep 2
 alice::ipsec up nat-t
-venus::sleep 2 
+venus::sleep 2
 venus::ipsec up nat-t
 venus::sleep 2