TT#12307 Adjust coreutils's `ls` output comparison for Debian/stretch

coreutils on jessie behaves like:

| sipwise@spce:~$ ls -la /var/cores/core.*
| ls: cannot access /var/cores/core.*: No such file or directory

... while on stretch we get:

| root@spce:~# ls -la /var/cores/core.*
| ls: cannot access '/var/cores/core.*': No such file or directory

Change-Id: Idb26193f28d0003a42a9fddf59dc5d06d630b6cf

ce/03_no-cores.yaml.tt2

@@ -3,4 +3,4 @@ command:
     exit-status: 2
     stdout: []
     stderr:
-      - "ls: cannot access /var/cores/core.*: No such file or directory"
+      - "/ls: cannot access '??/var/cores/core.*'??: No such file or directory/"