erp5_maileva_connector: small improvement

1. don't manipulate data base to avoid resend to web service in case of data base conflict
2. use existing property
3. change alarm frequency
12 jobs for master in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:35:07

passed ERP5.PerformanceTest-Master

00:25:45

failed ERP5.UnitTest-Master

01:04:01

failed ERP5.UnitTest-Master.Medusa

03:57:57

passed SlapOS.Eggs.UnitTest-Master.Python2

00:10:40

passed SlapOS.Eggs.UnitTest-Master.Python3

00:12:16

failed ERP5.UnitTest-Master

01:09:38

failed ERP5.UnitTest-Master

01:17:25

passed SlapOS.Eggs.UnitTest-Master.Python2

00:11:10

passed SlapOS.Eggs.UnitTest-Master.Python2

00:11:26

passed SlapOS.Eggs.UnitTest-Master.Python3

00:12:05

passed SlapOS.Eggs.UnitTest-Master.Python3

00:23:21