release validation: Python Leaderboard with DirectRunner fails

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* Running Python Leaderboard with DirectRunner
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/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/apache_beam/__init__.py:84: UserWarning: You are using Apache Beam with Python 2. New releases of Apache Beam will soon support Python 3 only.
  'You are using Apache Beam with Python 2. '
INFO:root:Missing pipeline option (runner). Executing pipeline using the default runner: DirectRunner.
/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/apache_beam/io/gcp/bigquery.py:1220: BeamDeprecationWarning: options is deprecated since First stable release. References to <pipeline>.options will not be supported
  experiments = p.options.view_as(DebugOptions).experiments or []
INFO:root:Running pipeline with DirectRunner.
/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/auth/_default.py:69: UserWarning: Your application has authenticated using end user credentials from Google Cloud SDK. We recommend that most server applications use service accounts instead. If your application continues to use end user credentials from Cloud SDK, you might receive a "quota exceeded" or "API not enabled" error. For more information about service accounts, see https://cloud.google.com/docs/authentication/
  warnings.warn(_CLOUD_SDK_CREDENTIALS_WARNING)
ERROR:concurrent.futures:exception calling callback for <Future at 0x7f7c6f37add0 state=finished raised IOError>
Traceback (most recent call last):
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/concurrent/futures/_base.py", line 331, in _invoke_callbacks
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/auth/transport/grpc.py", line 75, in wrapped
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/concurrent/futures/_base.py", line 455, in result
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/concurrent/futures/thread.py", line 63, in run
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/auth/transport/grpc.py", line 67, in _get_authorization_headers
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/auth/credentials.py", line 124, in before_request
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/oauth2/credentials.py", line 182, in refresh
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/oauth2/_client.py", line 248, in refresh_grant
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/oauth2/_client.py", line 105, in _token_endpoint_request
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/google/auth/transport/requests.py", line 169, in __call__
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/requests/sessions.py", line 533, in request
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/requests/sessions.py", line 646, in send
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/requests/adapters.py", line 416, in send
  File "/tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/requests/adapters.py", line 228, in cert_verify
IOError: Could not find a suitable TLS CA certificate bundle, invalid path: /tmp/beam-release.2.18.0.DCDdsy/beam_env_python2.7/local/lib/python2.7/site-packages/certifi/cacert.pem