Issue #25940: Use self-signed.pythontest.net in SSL tests

Issue #25940: Use self-signed.pythontest.net in SSL tests

This is instead of svn.python.org, whose certificate recently expired, and
whose new certificate uses a different root certificate.

The certificate used at the pythontest server was modifed to set the "basic
constraints" CA flag. This flag seems to be required for test_get_ca_certs_
capath() to work.

Added the new self-signed certificate to capath with the following commands:

cp Lib/test/{selfsigned_pythontestdotnet.pem,capath/}
c_rehash -v Lib/test/capath/
c_rehash -v -old Lib/test/capath/
# Note the generated file names
cp Lib/test/capath/{selfsigned_pythontestdotnet.pem,0e4015b9.0}
mv Lib/test/capath/{selfsigned_pythontestdotnet.pem,ce7b8643.0}

When attempting to connect to port 444 on the new server, the resulting error
code is EHOSTUNREACH on Linux, and ETIMEDOUT on Windows.