make ls command run in warn_only flag so it doesn't exit
make ls command run in warn_only flag so it doesn't exit

the whole issue script exits when sudo ls command returns a failure,
this fix will prevent that
Closes-Bug: #1680271

Change-Id: I295c73639f8cc8411fadcf8fadfb55e927114e45

Juniper/contrail-fabric-utils,Juniper/contrail-fabric-utils