tests: Fix Flaky system-tests "omit connection tracking ..."

While conntrack entries were flushed between the sub-tests, flows from
previous tests might still be present, causing conntrack entries to be
re-created.

Fixes: a0f82ef ("northd: bypass connection tracking for stateless flows when there are LB flows present")
Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Acked-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
(cherry picked from commit eacd7dc)

tests/system-ovn.at

@@ -9067,7 +9067,7 @@ ovn-nbctl ls-lb-del foo lb1
 
 # add stateless acl
 check ovn-nbctl acl-add foo from-lport 1 1 allow-stateless
-check ovn-nbctl acl-add foo to-lport 1 1 allow-stateless
+check ovn-nbctl --wait=hv acl-add foo to-lport 1 1 allow-stateless
 
 AT_CHECK([ip netns exec foo1 wget   192.168.2.2 -t 3 -T 1], [0], [ignore], [ignore])
 
@@ -9212,7 +9212,7 @@ ovn-nbctl ls-lb-del foo lb1
 
 # add stateless acl
 check ovn-nbctl acl-add foo from-lport 1 1 allow-stateless
-check ovn-nbctl acl-add foo to-lport 1 1 allow-stateless
+check ovn-nbctl --wait=hv acl-add foo to-lport 1 1 allow-stateless
 
 AT_CHECK([ip netns exec foo1  wget http://[[fd12::2]] -t 3 -T 1], [0], [ignore], [ignore])