Enforce ssl_cert_reqs='required' by default

[u2mejc]

This resolves #1016

[u2mejc]

In testing this with a coworker, he pointed out that it's also not possible to use ssl.wrap_socket without passing the ca_certs. This makes the code rigid as it may not be possible the change cert providers without updating your python code.

Example: to accept the current default AWS Elasticache cert on ubuntu, you need to set:
r = redis.StrictRedis(host, ssl=True, ssl_ca_certs='/usr/share/ca-certificates/mozilla/Starfield_Class_2_CA.crt')

[andymccurdy]

Thanks. Merging this now.

[edmorley]

Hi :-)

This was listed under "other changes" in the release notes rather than "backwards incompatible changes", which meant we missed this change when reviewing the upgrade, which resulted in breakage in our staging environment until rolled back (Heroku Redis instances don't support strict SSL at present unfortunately).

Could the release notes be updated?

[andymccurdy]

@edmorley Thanks for the heads up. Updated the release notes.