Update all test certs and keys to use future proof crypto settings:
* 3072 bit RSA keys
* SHA-256 signature
Signed-off-by: Christian Heimes <christian@python.org>
Add test certs and test for ECDSA cert and EC/RSA dual mode.
I'm also adding certs for IDNA 2003/2008 tests and simplify some test
data handling.
Signed-off-by: Christian Heimes <christian@python.org>