Update SslConnector cipher list

Based off of python/cpython#3532, we use OpenSSL's default cipher list
and turn of things we don't like. This can't be used with 1.0.1,
however, which had a poor default set. There, we use the old defaults,
with the bits that aren't implemented in 1.0.1 removed (namely TLSv1.3
suites and ChaCha).