gnulib-tool.py: Don't leave temporary directories on exit. * pygnulib/main.py (main_with_exception_handling): Use tempfile.TemporaryDirectory as a context manager so it is removed before the program exits. (main): Expect a temporary directory to be passed as an argument. * pygnulib/GLConfig.py (GLConfig.__init__): Accept an optional temporary directory parameter instead of creating one. * pygnulib/GLImport.py (GLImport.__init__): Don't remove the cache's temporary directory since it doesn't create one anymore. (GLImport.execute): Don't remove the temporary directory explicitly. It is handled by the usage of a context manager. * pygnulib/GLTestDir.py (GLTestDir.execute, GLMegaTestDir.execute): Likewise.