Fix MLFlowLogger test

[ngcgarcia]

What does this PR do?

test_mlflow_ignore_hyperparameters is flakey--it passed tests on PR submission but later failed:

        # should not see num_cpus_per_node, num_nodes, mlflow_run_id
        expected_params_list = [
            'node_name',
            'rank_zero_seed',
            'composer_version',
            'composer_commit_hash',
            'mlflow_experiment_id',
        ]
>       assert set(expected_params_list) == set(actual_params_list)
E       AssertionError: assert {'composer_co...nk_zero_seed'} == {'composer_version'}
E         Extra items in the left set:
E         'node_name'
E         'composer_commit_hash'
E         'mlflow_experiment_id'
E         'rank_zero_seed'
E         Full diff:
E           {
E         +  'composer_commit_hash',
E            'composer_version',
E         +  'mlflow_experiment_id',
E         +  'node_name',
E         +  'rank_zero_seed',
E           }

This test was copied almost directly from test_mlflow_logging_works with a few commands removed because they were thought to be unnecessary (and some changes made for ignoring some hyperparameters).

The suspected culprit is the removal of the sleep. This small pause gave time for async logging to finish, and this test would nondeterministically fail because we didn't let it finish up logging (missing parameters that should be there).

What issue(s) does this change relate to?

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