add assert to ping test

Change-Id: I24055036e6d45b5eff1cd127e2a2c78485287587
Closes-Bug: #1818233
diff --git a/neutron_tempest_plugin/scenario/base.py b/neutron_tempest_plugin/scenario/base.py
index cc1ca4c..ffb4dbd 100644
--- a/neutron_tempest_plugin/scenario/base.py
+++ b/neutron_tempest_plugin/scenario/base.py
@@ -340,6 +340,11 @@
                       'reachable' if should_succeed else 'unreachable'
                   })
         result = test_utils.call_until_true(ping, timeout, 1)
+
+        # To make sure ping_ip_address called by test works
+        # as expected.
+        self.assertTrue(result)
+
         LOG.debug('%(caller)s finishes ping %(ip)s in %(timeout)s sec and the '
                   'ping result is %(result)s', {
                       'caller': caller, 'ip': ip_address, 'timeout': timeout,