python/tests: turn GraphError into failure inside of test_verify()

python/tests: turn GraphError into failure inside of test_verify()

That test was already marked as flapping in commit
5a73f904e192c44e304850287ac439d0b52f7be5.

However the test generates an UNEXPECTED(error)
instead of an UNEXPECTED(failure).

  [67(594)/75 at 36m28s] samba.tests.kcc.python3(vampire_dc)
  repsFrom source DSA guid (62f01940-a784-4e60-947a-a661c787c8cc) not found
  repsFrom source DSA guid (62f01940-a784-4e60-947a-a661c787c8cc) not found
  repsFrom source DSA guid (62f01940-a784-4e60-947a-a661c787c8cc) not found
  repsFrom source DSA guid (62f01940-a784-4e60-947a-a661c787c8cc) not found
  repsFrom source DSA guid (62f01940-a784-4e60-947a-a661c787c8cc) not found
  UNEXPECTED(error): samba.tests.kcc.python3.samba.tests.kcc.KCCTests.test_verify(vampire_dc)
  REASON: Exception: Exception: Traceback (most recent call last):
    File "bin/python/samba/tests/kcc/__init__.py", line 80, in test_verify
      attempt_live_connections=False)
    File "bin/python/samba/kcc/__init__.py", line 2659, in run
      ('connected',))
    File "bin/python/samba/kcc/__init__.py", line 2513, in plot_all_connections
      vertex_colors=vertex_colours)
    File "bin/python/samba/kcc/graph_utils.py", line 334, in verify_and_dot
      for p, e, doc in errors)))
  samba.kcc.graph_utils.GraphError: The 'dsa_final CN=NTDS Settings,CN=LOCALVAMPIREDC,CN=Servers,CN=Default-First-Site-Name,CN=Sites,CN=Configuration,DC=samba,DC=example,DC=com' graph lacks the following properties:
  connected: the graph is not connected, as the following vertices are unreachable:

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>