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/crl-from-cache/pretest.dat

@@ -4,5 +4,5 @@ carol::wget -q http://crl.strongswan.org/strongswan.crl
 carol::mv strongswan.crl /etc/ipsec.d/crls/5da7dd700651327ee7b66db3b5e5e060ea2e4def.crl
 moon::ipsec start
 carol::ipsec start
-carol::sleep 2
+carol::expect-connection home
 carol::ipsec up home