FastAvroTest has slow test_dynamic_exhaustive on Python 2 and 3.

GLOB sdist-make: /app/sdks/python/setup.py
py27 inst-nodeps: /app/sdks/python/target/.tox/.tmp/package/1/apache-beam-2.14.0.dev0.zip
...
warning: no files found matching 'LICENSE'
writing manifest file 'apache_beam.egg-info/SOURCES.txt'
test_dynamic_work_rebalancing_exhaustive (apache_beam.io.avroio_test.TestFastAvro) ... ok

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XML: /app/sdks/python/nosetests.xml
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Ran 1 test in 444.705s

OK
py27 run-test-post: commands[0] | /app/sdks/python/scripts/run_tox_cleanup.sh
py35 inst-nodeps: /app/sdks/python/target/.tox/.tmp/package/1/apache-beam-2.14.0.dev0.zip
...
warning: no files found matching 'LICENSE'
writing manifest file 'apache_beam.egg-info/SOURCES.txt'
/app/sdks/python/apache_beam/__init__.py:84: UserWarning: Running the Apache Beam SDK on Python 3 is not yet fully supported. You may encounter buggy behavior or missing features.
  'Running the Apache Beam SDK on Python 3 is not yet fully supported. '
test_dynamic_work_rebalancing_exhaustive (apache_beam.io.avroio_test.TestFastAvro) ... ok

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XML: /app/sdks/python/nosetests.xml
----------------------------------------------------------------------
Ran 1 test in 385.768s

OK
py35 run-test-post: commands[0] | /app/sdks/python/scripts/run_tox_cleanup.sh
___________________________________ summary ____________________________________
  py27: commands succeeded
  py35: commands succeeded
  congratulations :)