**What happened**:

With the new Backport providers, when calling `DataflowCreatePythonJobOperator` with an empty `py_rerquirments` Dataflow commands always launch inside a virtualenv.

**What you expected to happen**:

The Dataflow command should run locally.


tests/providers/google/cloud/operators/test_dataflow.py
"""Test DataflowHook is created and the right args are passed to
        start_template_workflow.
        """
        start_template_hook = dataflow_mock.return_value.start_template_dataflow
        self.dataflow.execute(None)
        self.assertTrue(dataflow_mock.called)
        expected_options = {
            'project': 'test',
            'stagingLocation': 'gs://test/staging',
            'tempLocation': 'gs://test/temp',
            'zone': 'us-central1-f',
            'EXTRA_OPTION': "TEST_A"
        }
        start_template_hook.assert_called_once_with(
            job_name=JOB_NAME,
            variables=expected_options,
            parameters=PARAMETERS,
            dataflow_template=TEMPLATE,
            on_new_job_id_callback=mock.ANY,
            project_id=None,
            location=TEST_LOCATION
        )