Avoid using readConcern snapshot in sharded transaction tests

 [2019/07/02 22:06:35.816] ======================================================================

 [2019/07/02 22:06:35.816] ERROR [0.051s]: test_transactions_transaction_options_defaultTransactionOptions_override_client_options (test_transactions.TestTransactions)

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 [2019/07/02 22:06:35.816] Traceback (most recent call last):

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/__init__.py", line 410, in wrap

 [2019/07/02 22:06:35.816]     return f(*args, **kwargs)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/__init__.py", line 410, in wrap

 [2019/07/02 22:06:35.816]     return f(*args, **kwargs)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/__init__.py", line 410, in wrap

 [2019/07/02 22:06:35.816]     return f(*args, **kwargs)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/test_transactions.py", line 342, in run_scenario

 [2019/07/02 22:06:35.816]     self.run_scenario(scenario_def, test)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/utils_spec_runner.py", line 507, in run_scenario

 [2019/07/02 22:06:35.816]     self.run_operations(sessions, collection, test['operations'])

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/utils_spec_runner.py", line 342, in run_operations

 [2019/07/02 22:06:35.816]     result = self.run_operation(sessions, collection, op.copy())

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/test/utils_spec_runner.py", line 293, in run_operation

 [2019/07/02 22:06:35.816]     result = cmd(**dict(arguments))

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/collection.py", line 697, in insert_one

 [2019/07/02 22:06:35.816]     session=session),

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/collection.py", line 611, in _insert

 [2019/07/02 22:06:35.816]     bypass_doc_val, session)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/collection.py", line 599, in _insert_one

 [2019/07/02 22:06:35.816]     acknowledged, _insert_command, session)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/mongo_client.py", line 1484, in _retryable_write

 [2019/07/02 22:06:35.816]     return self._retry_with_session(retryable, func, s, None)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/mongo_client.py", line 1385, in _retry_with_session

 [2019/07/02 22:06:35.816]     return func(session, sock_info, retryable)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/collection.py", line 594, in _insert_command

 [2019/07/02 22:06:35.816]     retryable_write=retryable_write)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/pool.py", line 612, in command

 [2019/07/02 22:06:35.816]     user_fields=user_fields)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/network.py", line 158, in command

 [2019/07/02 22:06:35.816]     parse_write_concern_error=parse_write_concern_error)

 [2019/07/02 22:06:35.816]   File "/data/mci/cb2ee5cd4b43659603d74a398e413f60/src/pymongo/helpers.py", line 155, in _check_command_response

 [2019/07/02 22:06:35.816]     raise OperationFailure(msg % errmsg, code, response)

 [2019/07/02 22:06:35.816] OperationFailure: Transaction 806c7df4-3cf3-4839-987a-b4206e3974e6:1 was aborted on statement 0 due to: a non-retryable snapshot error :: caused by :: Encountered error from localhost:27217 during a transaction :: caused by :: Read timestamp Timestamp(1562119591, 69) is older than the oldest available timestamp.

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