slapos_cloud: reduce the risk of always allocating on the same node

13 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS-Master.UnitTest-Master

02:53:12

failed SlapOS.Eggs.UnitTest-Master.Python2

00:23:46

passed SlapOS.Eggs.UnitTest-Master.Python3

00:29:02

failed SlapOS-Master.UnitTest-Master

03:10:27

failed SlapOS-Master.UnitTest-Master

02:45:10

failed SlapOS-Master.UnitTest-Master

02:44:22

passed SlapOS.Eggs.UnitTest-Master.Python2

00:25:10

passed SlapOS.Eggs.UnitTest-Master.Python2

00:26:24

failed SlapOS.Eggs.UnitTest-Master.Python3

00:27:28

passed SlapOS.Eggs.UnitTest-Master.Python3

02:17:23

failed SlapOS.Eggs.UnitTest-Master.Python3

00:28:33

failed SlapOS.Eggs.UnitTest-Master.Python3

failed SlapOS.Eggs.UnitTest-Master.Python3

00:27:59