Update the Python tests for remaining modules

...ors/Vtkm/Filters/Testing/Python/TestVTKMAverageToCells.py

...rs/Vtkm/Filters/Testing/Python/TestVTKMAverageToPoints.py

Accelerators/Vtkm/Filters/Testing/Python/TestVTKMSlice.py

Charts/Core/Testing/Python/TestBarGraph.py

Charts/Core/Testing/Python/TestLinePlot.py

Charts/Core/Testing/Python/TestLinePlotColors.py

Charts/Core/Testing/Python/TestParallelCoordinatesColors.py

Charts/Core/Testing/Python/TestScatterPlotColors.py

Charts/Core/Testing/Python/TestStackedPlot.py

Domains/Microscopy/Testing/Python/testOpenSlideReader.py

Parallel/Core/Testing/Python/TestPolyDataPieces.py

Parallel/Core/Testing/Python/TestSockets.py

Parallel/Core/Testing/Python/TestUnstructuredPieces.py

Parallel/MPI4Py/Testing/Python/TestParallelNumpy.py

Web/Core/Testing/Python/TestDataEncoder.py

Web/Core/Testing/Python/TestObjectIdMap.py

Web/Core/Testing/Python/TestWebApplicationMemory.py

Web/Python/Testing/Python/TestSerializeRenderWindow.py

Web/Python/vtkmodules/web/testing.py