[3406] Fixed cleanup in signal handling tests for DHCPv6.

src/bin/dhcp6/tests/dhcp6_test_func.sh

@@ -40,7 +40,7 @@ set_logger() {
 _GET_PIDS=     # Holds space separated list of DHCPv6 pids.
 _GET_PIDS_NUM= # Holds the number of DHCPv6 server pids.
 get_pids() {
-    _GET_PIDS=`ps -o pid,command | grep b10-dhcp6 | grep -v grep | awk '{print $1}'`
+    _GET_PIDS=`ps -ax -o pid,command | grep b10-dhcp6 | grep -v grep | awk '{print $1}'`
     _GET_PIDS_NUM=`printf "%s" "${_GET_PIDS}" | wc -w | awk '{print $1}'`
 }