How did OpenSSL get like that? Ubuntu 14.04 comes with OpenSSL 1.0.1f, but you have 1.1.0e.
OPENSSL_sk_num was added in 1.1.0; i’d guess that the Python cryptography module got compiled against 1.1.0e (headers in /usr/local/include, perhaps?) but is running against 1.0.1f (in /usr/lib).
I don’t have any suggestions for how to fix it, though.