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/dynamic-initiator/posttest.dat

@@ -1,6 +1,5 @@
 dave::ipsec stop
 carol::ipsec stop
-dave::sleep 1
 moon::ipsec stop
 moon::iptables-restore < /etc/iptables.flush
 carol::iptables-restore < /etc/iptables.flush