tests: use iptables --wait
tests: use iptables --wait

QubesOS/qubes-issues#3665 affects also tests...

marmarek/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin