Offload conntrack testcases. Sleep after stopping iperf

This sleep is important to be sure that there are no packets in the
network that may break next testcase

Without this sleep, sometimes there are problems deleting vms and
makes fail next testcases. It is like the message to delete the
vm is lost and tempest waits until the timeout to remove vm
expires.

Change-Id: Icd138f3ce69e5aef92ed1d0be73707ba49e8161f
(cherry picked from commit c9180b9)

nfv_tempest_plugin/tests/scenario/test_nfv_offload.py

@@ -942,6 +942,11 @@ def check_conntrack(self, srv_pair, protocol):
 
         for item in iperf_logs:
             shell_utils.stop_iperf(item['server'], item['log_file'])
+        # sleep for a while to be sure that after stopping iperf,
+        # there is no packet generated by iperf that may break
+        # the following test
+        time.sleep(10)
+
         return errors
 
     def check_conntrack_table(self, hyper, source, protocol, l4_port):