Respect ONOS_USER and ONOS_GROUP settings as intended.

Change-Id: I89936604434aa9c22d128350ac452e1aab763d5e

@@ -110,7 +110,7 @@ function cell {
         [ ! -f $ONOS_ROOT/tools/test/cells/$1 ] && \
             echo "No such cell: $1" >&2 && return 1
         unset ONOS_CELL ONOS_NIC ONOS_IP ONOS_APPS ONOS_BOOT_FEATURES
-        unset OCI OCN OCT ONOS_INSTANCES ONOS_FEATURES ONOS_USER ONOS_GROUP
+        unset OCI OCN OCT ONOS_INSTANCES ONOS_FEATURES
         unset $(env | sed -n 's:\(^OC[0-9]\{1,\}\)=.*:\1 :g p')
         export ONOS_USER=${ONOS_USER:-sdn}
         export ONOS_GROUP=${ONOS_GROUP:-sdn}