testing: Remove nearly all sleep calls from pretest and posttest scripts

By consistently using the `expect-connection` helper we can avoid pretty
much all previously needed calls to sleep.

testing/tests/ikev2/any-interface/pretest.dat

@@ -4,7 +4,8 @@ alice::ipsec start
 moon::ipsec start
 sun::ipsec start
 bob::ipsec start
-moon::sleep 2 
+moon::expect-connection alice
 moon::ping -n -c 3 -s 8184 -p deadbeef PH_IP_ALICE
 moon::ping -n -c 3 -s 8184 -p deadbeef PH_IP_SUN
+bob::expect-connection sun
 bob::ping -n -c 3 -s 8184 -p deadbeef PH_IP_SUN1