autobuild[sn-devel-184]: intermittent test failure detected

[autobuild]

The autobuild test system (on sn-devel-184) has detected an intermittent failing test in 
the current master tree.

The autobuild log of the failure is available here:

   https://git.samba.org/autobuild.flakey.sn-devel-184/2019-04-14-0344/flakey.log

The failure seems to be in the "samba-ad-dc-ntvfs" suite, whose build logs are available here:

   https://git.samba.org/autobuild.flakey.sn-devel-184/2019-04-14-0344/samba-ad-dc-ntvfs.stderr
   https://git.samba.org/autobuild.flakey.sn-devel-184/2019-04-14-0344/samba-ad-dc-ntvfs.stdout
  
The top commit at the time of the failure was:

commit 98521ce51c64045ca651ed72440a3224648ce00e
Author: Stefan Metzmacher <metze at samba.org>
Date:   Wed Feb 27 14:23:48 2019 +0100

    .gitlab-ci.yml: show the system state also as after_script
    
    Signed-off-by: Stefan Metzmacher <metze at samba.org>
    Reviewed-by: Andreas Schneider <asn at samba.org>
    Reviewed-by: Ralph Boehme <slow at samba.org>
    
    Autobuild-User(master): Stefan Metzmacher <metze at samba.org>
    Autobuild-Date(master): Fri Apr 12 20:42:27 UTC 2019 on sn-devel-144

and the last 50 lines of the stdout log were:

[216(857)/252 at 16m58s] samba4.smb.signing on with -k yes --signing=required(ad_dc_ntvfs)
[217(858)/252 at 16m58s] samba4.smb.signing on with -k yes --option=gensec:fake_gssapi_krb5=yes --option=gensec:gssapi_krb5=no --signing=on(ad_dc_ntvfs)
[218(859)/252 at 16m59s] samba4.smb.signing on with -k yes --option=gensec:fake_gssapi_krb5=yes --option=gensec:gssapi_krb5=no --signing=required(ad_dc_ntvfs)
[219(860)/252 at 16m59s] samba4.smb.signing --signing=yes anon(ad_dc_ntvfs)
[220(861)/252 at 16m59s] samba4.smb.signing --signing=required anon(ad_dc_ntvfs)
[221(862)/252 at 17m0s] samba.tests.complex_expressions(ad_dc_ntvfs)
[222(884)/252 at 17m6s] samba.tests.samba_tool.gpo(ad_dc_ntvfs:local)
[223(896)/252 at 17m35s] samba.tests.dcerpc.registry(ad_dc_ntvfs:local)
[224(899)/252 at 17m35s] samba.tests.dcerpc.dnsserver(ad_dc_ntvfs)
[225(916)/252 at 17m48s] samba.tests.auth_log(ad_dc_ntvfs:local)
[226(963)/252 at 17m56s] samba.tests.auth_log_pass_change(ad_dc_ntvfs)
[227(971)/252 at 18m3s] samba.tests.auth_log_ncalrpc(ad_dc_ntvfs:local)
[228(973)/252 at 18m3s] samba.tests.auth_log_samlogon(ad_dc_ntvfs:local)
[229(974)/252 at 18m4s] samba.tests.auth_log_netlogon(ad_dc_ntvfs:local)
[230(975)/252 at 18m5s] samba.tests.auth_log_netlogon_bad_creds(ad_dc_ntvfs:local)
[231(979)/252 at 18m7s] samba.tests.password_hash_fl2008(ad_dc_ntvfs:local)
[232(983)/252 at 18m9s] samba.tests.krb5_credentials(ad_dc_ntvfs)
[233(986)/252 at 18m11s] samba.tests.py_credentials(ad_dc_ntvfs)
[234(994)/252 at 18m14s] samba.tests.emulate.traffic(ad_dc_ntvfs)
[235(996)/252 at 18m14s] samba.tests.emulate.traffic_packet(ad_dc_ntvfs)
[236(1085)/252 at 19m19s] samba.tests.blackbox.traffic_replay(ad_dc_ntvfs)
[237(1090)/252 at 19m41s] samba.tests.blackbox.traffic_learner(ad_dc_ntvfs)
[238(1092)/252 at 19m42s] samba.tests.blackbox.traffic_summary(ad_dc_ntvfs)
[239(1092)/252 at 19m43s] samba.tests.blackbox.smbcontrol(ad_dc_ntvfs:local)
[240(1094)/252 at 19m44s] samba4.urgent_replication.python(ad_dc_ntvfs)(ad_dc_ntvfs:local)
[241(1102)/252 at 19m48s] samba4.ldap.match_rules.python(ad_dc_ntvfs)
[242(1136)/252 at 20m11s] samba4.ldap.notification.python(ad_dc_ntvfs)(ad_dc_ntvfs)
UNEXPECTED(failure): samba4.ldap.notification.python(ad_dc_ntvfs).__main__.LDAPNotificationTest.test_simple_search(ad_dc_ntvfs)
REASON: Exception: Exception: Traceback (most recent call last):
  File "/memdisk/autobuild/fl/b285913/samba-ad-dc-ntvfs/source4/dsdb/tests/python/notification.py", line 151, in test_simple_search
    self.assertIsNotNone(msg3)
AssertionError: unexpectedly None

FAILED (1 failures, 0 errors and 0 unexpected successes in 0 testsuites)

A summary with detailed information can be found in:
  ./bin/ab/summary
TOP 10 slowest tests
samba4.raw.notify(ad_dc_ntvfs) -> 109
samba4.nbt.winsreplication(ad_dc_ntvfs) -> 73
samba.tests.emulate.traffic_packet(ad_dc_ntvfs) -> 65
samba4.ntvfs.cifs.krb5.base.deny2(ad_dc_ntvfs) -> 58
samba4.base.deny2(ad_dc_ntvfs) -> 57
samba4.ntvfs.cifs.krb5.base.deny1(ad_dc_ntvfs) -> 53
samba4.base.deny1(ad_dc_ntvfs) -> 52
samba4.raw.oplock(ad_dc_ntvfs) -> 32
samba4.smb2.oplock(ad_dc_ntvfs) -> 31
samba.tests.samba_tool.gpo(ad_dc_ntvfs:local) -> 28
ERROR: test failed with exit code 1
Makefile:16: recipe for target 'test' failed