Fixes CoProcessingTestPythonScript test in static builds.

vtkCPPythonScriptPipeline was not uninitializing Python interpretor at the
right time. That was resulting it memory corruption. Tweaked the logic in
vtkCPPythonScriptPipeline to release Python interpretor when the last
vtkCPPythonScriptPipeline instace is deleted.

Change-Id: I912bf7363f5d8315024cf7b0063e88df530a0d0d
Merge topic 'clean_coprocessing_python' into next

aaa5372 Fixes CoProcessingTestPythonScript test in static builds.