We had this failure a lot in the past and it seems to be resolve, but I see it again today:

======================================================================
FAIL: test_add_delete_ipv6 (network.ip_address_test.IPAddressTest)
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Traceback (most recent call last):
  File "/home/jenkins/workspace/vdsm_standard-check-patch/vdsm/tests/testValidation.py", line 333, in wrapper
    return f(*args, **kwargs)
  File "/home/jenkins/workspace/vdsm_standard-check-patch/vdsm/tests/network/ip_address_test.py", line 226, in test_add_delete_ipv6
    self._test_add_delete(IPV6_A_WITH_PREFIXLEN, IPV6_B_WITH_PREFIXLEN)
  File "/home/jenkins/workspace/vdsm_standard-check-patch/vdsm/tests/network/ip_address_test.py", line 247, in _test_add_delete
    self._assert_has_no_address(nic, ip_b)
  File "/home/jenkins/workspace/vdsm_standard-check-patch/vdsm/tests/network/ip_address_test.py", line 344, in _assert_has_no_address
    self._assert_address_not_in(address_with_prefixlen, addresses)
  File "/home/jenkins/workspace/vdsm_standard-check-patch/vdsm/tests/network/ip_address_test.py", line 352, in _assert_address_not_in
    self.assertNotIn(address_with_prefixlen, addresses_list)
AssertionError: '2002:99::1/64' unexpectedly found in ['2002:99::1/64', '2001:99::1/64', 'fe80::6:23ff:fead:ed34/64']
-------------------- >> begin captured logging << --------------------
2019-01-04 16:01:53,543 DEBUG (MainThread) [root] /sbin/ip link add name dummy_NKzY1 type dummy (cwd None) (cmdutils:133)
2019-01-04 16:01:53,559 DEBUG (MainThread) [root] SUCCESS: <err> = ''; <rc> = 0 (cmdutils:141)
2019-01-04 16:01:53,563 DEBUG (netlink/events) [root] START thread <Thread(netlink/events, started daemon 139806010234624)> (func=<bound method Monitor._scan of <vdsm.network.netlink.monitor.Monitor object at 0x7f271d654cd0>>, args=(), kwargs={}) (concurrent:193)
2019-01-04 16:01:53,567 DEBUG (MainThread) [root] /sbin/ip link set dev dummy_NKzY1 up (cwd None) (cmdutils:133)
2019-01-04 16:01:53,586 DEBUG (MainThread) [root] SUCCESS: <err> = ''; <rc> = 0 (cmdutils:141)
2019-01-04 16:01:53,593 DEBUG (netlink/events) [root] FINISH thread <Thread(netlink/events, started daemon 139806010234624)> (concurrent:196)
2019-01-04 16:01:53,597 DEBUG (MainThread) [root] /sbin/ip -6 addr add dev dummy_NKzY1 2001:99::1/64 (cwd None) (cmdutils:133)
2019-01-04 16:01:53,615 DEBUG (MainThread) [root] SUCCESS: <err> = ''; <rc> = 0 (cmdutils:141)
2019-01-04 16:01:53,620 DEBUG (MainThread) [root] /sbin/ip -6 addr add dev dummy_NKzY1 2002:99::1/64 (cwd None) (cmdutils:133)
2019-01-04 16:01:53,632 DEBUG (MainThread) [root] SUCCESS: <err> = ''; <rc> = 0 (cmdutils:141)
2019-01-04 16:01:53,639 DEBUG (MainThread) [root] /sbin/ip -6 addr del dev dummy_NKzY1 2002:99::1/64 (cwd None) (cmdutils:133)
2019-01-04 16:01:53,656 DEBUG (MainThread) [root] SUCCESS: <err> = ''; <rc> = 0 (cmdutils:141)
2019-01-04 16:01:53,670 DEBUG (MainThread) [root] /sbin/ip link del dev dummy_NKzY1 (cwd None) (cmdutils:133)
2019-01-04 16:01:53,705 DEBUG (MainThread) [root] SUCCESS: <err> = ''; <rc> = 0 (cmdutils:141)
--------------------- >> end captured logging << ---------------------

Build: