MDAnalysisTests.analysis.test_encore.TestEncore. test_dres_without_superimposition fails randomly

[xiki-tempula]

test_dres_without_superimposition fails randomly as is seen in https://travis-ci.com/MDAnalysis/mdanalysis/jobs/162709617 from PR #2087 .

The error message goes as:

    def test_dres_without_superimposition(self, ens1, ens2):
        distance_matrix = encore.get_distance_matrix(
            encore.merge_universes([ens1, ens2]),
            superimpose=False)
        results, details = encore.dres([ens1, ens2],
                                       distance_matrix = distance_matrix)
        result_value = results[0,1]
        expected_value = 0.68
        assert_almost_equal(result_value, expected_value, decimal=1,
>                           err_msg="Unexpected value for Dim. reduction Ensemble Similarity: {0:f}. Expected {1:f}.".format(result_value, expected_value))
E       AssertionError: 
E       Arrays are not almost equal to 1 decimals
E       Unexpected value for Dim. reduction Ensemble Similarity: 0.606882. Expected 0.680000.
E        ACTUAL: 0.60688156691445183
E        DESIRED: 0.68
testsuite/MDAnalysisTests/analysis/test_encore.py:303: AssertionError

[orbeckst]

See #1933 for discussion.