add basic ipv6 check

tests/cern_basic/5_check_ipv6.sh

+#!/bin/sh
+# Author: Ben Morrice <ben.morrice@cern.ch>
+
+t_Log "Running $0 - Checking ipv6"
+
+if [ -f /proc/net/if_inet6 ]; then
+  echo "Running kernel is IPv6 ready, running ping6 to cern.ch"
+  ping6 -c1 cern.ch
+else
+  echo "Running kernel does not support IPv6"
+fi
+t_CheckExitStatus $?