bpo-38271: encrypt private key test files with AES256 (GH-16385)

The private keys for test_ssl were encrypted with 3DES in traditional
PKCS#5 format. 3DES and the digest algorithm of PKCS#5 are blocked by
some strict crypto policies. Use PKCS#8 format with AES256 encryption
instead.

Signed-off-by: Christian Heimes <christian@python.org>



https://bugs.python.org/issue38271



Automerge-Triggered-By: @tiran