fix "stack/caucase: Fix md5 change detection"

Make the md5 detection fix python3 compatible.

Fixes 4e5a9ee4
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:37

passed SlapOS.SlapRunner.ResilienceTest-Master

00:22:26

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:17:38

passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:27

passed SlapOS.Eggs.UnitTest-Master.Python3

01:19:33