bpo-35925: Skip SSL tests that fail due to weak external certs. (GH-13124)

bpo-35925: Skip SSL tests that fail due to weak external certs. (GH-13124)

Modern Linux distros such as Debian Buster have default OpenSSL system
configurations that reject connections to servers with weak certificates
by default.  This causes our test suite run with external networking
resources enabled to skip these tests when they encounter such a failure.

Fixing the network servers is a separate issue.
(cherry picked from commit 2cc0223f43a1ffd59c887a73e2b0ce5202f3be90)

Co-authored-by: Gregory P. Smith <greg@krypto.org>