[test] when the config change, we should cleanup sys.path and sys.modules. Closes #3634164 Without this, modules imported within instance home will be messed up.

[wsgi] make sure request.content is available for consumption The wsgi.input stream is not seekable, so make a copy either to memory or disk so it's still available to the user even after we've parsed it (for POST form processing). Closes #3554996