testing: Use expect-connection in swanctl scenarios

Only in net2net-start do we have to use `sleep` to ensure the SA is
up when the tests are running.

testing/tests/swanctl/net2net-cert/pretest.dat

@@ -2,5 +2,6 @@ moon::iptables-restore < /etc/iptables.rules
 sun::iptables-restore < /etc/iptables.rules
 moon::service charon start 2> /dev/null
 sun::service charon start 2> /dev/null
-moon::sleep 1
+moon::expect-connection gw-gw
+sun::expect-connection gw-gw
 moon::swanctl --initiate --child net-net 2> /dev/null