tests: fix slirp flake v2

Commit 4a45167 points at the correct error source however the fix
for it was not working. ls -l will alwys look differnt when called on
different paths. We only want to compare the actual link target. Fix
this by using readlink.

Fixes containers#110

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

test/helpers.bash

@@ -297,7 +297,7 @@ function create_netns() {
     # we have to wait for unshare and check that we have a new ns before returning
     local timeout=2
     while [[ $timeout -gt 1 ]]; do
-        if [[ "$(ls -l /proc/self/ns/net)" != "$(ls -l /proc/$pid/ns/net)" ]]; then
+        if [ "$(readlink /proc/self/ns/net)" != "$(readlink /proc/$pid/ns/net)" ]; then
             echo $pid
             return
         fi