prune: fix some UnicodeDecodeError on python3 with binary scripts

Some softwares have some binary executables in builout bin folder,
reading them as text can fail. In this case we can ignore them.
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-Master.Python2

00:33:38

passed SlapOS.Eggs.UnitTest-Master.Python3

00:26:37

failed SlapOS.Eggs.UnitTest-Master.Python2

00:23:46

failed SlapOS.Eggs.UnitTest-Master.Python2

00:42:56

passed SlapOS.Eggs.UnitTest-Master.Python3

01:10:10

passed SlapOS.Eggs.UnitTest-Master.Python3

01:53:54