Synchronize some distutils tests with 3.2.

Synchronize some distutils tests with 3.2.

- Actually check the contents of the file created by bdist_dumb.
- Don’t use “RECORD” as filename for non-PEP 376 record file
- Don’t start method name with “_test”, it looks like a disabled test
  method instead of an helper method
- Fix some idioms (assertIn, addCleanup)