PYTHON-989 - Fix find_one_and_write_concern test when run with authentication.

Author: Luke Lovett

test/test_collection.py

@@ -2003,6 +2003,9 @@ def test_find_one_and_write_concern(self):
  # default WriteConcern.
  c_default = db.get_collection('test', write_concern=WriteConcern())
  results = listener.results
+ # Authenticate the client and throw out auth commands from the listener.
+ db.command('ismaster')
+ results.clear()
  try:
  if client_context.version.at_least(3, 1, 9, -1):
  c_w0.find_and_modify(