erp5_trade: use quantity variable to have testPackingListRoundingPrecision test working

11 jobs for master in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
failed ERP5.CodingStyleTest-Master

01:35:51

passed ERP5.PerformanceTest-Master

00:25:56

failed ERP5.UnitTest-Master

01:44:21

failed ERP5.UnitTest-Master.Medusa

02:17:49

passed SlapOS.Eggs.UnitTest-Master.Python2

00:17:41

passed SlapOS.Eggs.UnitTest-Master.Python3

00:21:38

failed ERP5.CodingStyleTest-Master

01:20:40

passed ERP5.PerformanceTest-Master

00:25:48

failed ERP5.UnitTest-Master

02:18:13

passed SlapOS.Eggs.UnitTest-Master.Python2

00:14:29

passed SlapOS.Eggs.UnitTest-Master.Python3

00:14:44