pyopenssl: 16.2.0 -> 17.0.0 and fix tests

Upstream changes:

 * Added OpenSSL.X509Store.set_time() to set a custom verification time
   when verifying certificate chains. pyca/pyopenssl#567
 * Added a collection of functions for working with OCSP stapling. None
   of these functions make it possible to validate OCSP assertions, only
   to staple them into the handshake and to retrieve the stapled
   assertion if provided. Users will need to write their own code to
   handle OCSP assertions. We specifically added:
   Context.set_ocsp_server_callback, Context.set_ocsp_client_callback,
   and Connection.request_ocsp. pyca/pyopenssl#580
 * Changed the SSL module's memory allocation policy to avoid zeroing
   memory it allocates when unnecessary. This reduces CPU usage and
   memory allocation time by an amount proportional to the size of the
   allocation. For applications that process a lot of TLS data or that
   use very lage allocations this can provide considerable performance
   improvements. pyca/pyopenssl#578
 * Automatically set SSL_CTX_set_ecdh_auto() on OpenSSL.SSL.Context.
   pyca/pyopenssl#575
 * Fix empty exceptions from OpenSSL.crypto.load_privatekey().
   pyca/pyopenssl#581

The full upstream changelog can be found at:

https://pyopenssl.readthedocs.io/en/17.0.0/changelog.html



I've also added a patch from pyca/pyopenssl#637 in order to fix the
tests, which was the main reason for the version bump because that patch
won't apply for 16.2.0.

According to the upstream changelog there should be no
backwards-incompatible changes, but I've tested building against some of
the packages depending on pyopenssl anyway. Regardless of this, the
build for pyopenssl fails right now anyway, so the worst that could
happen via this commit would be that we break something that's already
broken.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>