tests: fixed "basic connectivity with multiple requested-chassis"

Tests was randomly failing as missing some packets (e.g
from Second arrives to hv2:Migrator)

Signed-off-by: Xavier Simonart <xsimonar@redhat.com>
Acked-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>

tests/ovn.at

@@ -14841,6 +14841,11 @@ wait_column "$hv1_uuid" Port_Binding requested_chassis logical_port=migrator
 wait_column "$hv2_uuid" Port_Binding additional_chassis logical_port=migrator
 wait_column "$hv2_uuid" Port_Binding requested_additional_chassis logical_port=migrator
 
+# Port should be up (and flows installed) when migration is completed on hv1.
+# However, neither ports up nor additional_chassis do guarantee that flows on hv2 are fully installed.
+# ovn-installed on hv2 should guarantee that.
+OVS_WAIT_UNTIL([test `as hv2 ovs-vsctl get Interface migrator external_ids:ovn-installed` = '"true"'])
+
 # check that...
 # unicast from First arrives to hv1:Migrator
 # unicast from First arrives to hv2:Migrator