Mock server test

[etataurov]

We need to test this library with real-like server.
This PR contains attempt to do that, but there are few things need to be fixed somehow

• Compile proper binary from https://github.com/CleverTap/go-apns-server
• Python 3.5: NotImplementedError: The ALPN extension requires OpenSSL 1.0.2 or later. We need to install updated openssl to travis
• Python 3.4: AttributeError: 'SSLContext' object has no attribute 'set_alpn_protocols' Thats an actual bug found by this test.
• add Python3.6 beta
• repair coveralls

[etataurov]

After a lot of trial and error here what we have:

• Python3.5 with recent OpenSSL works great
• Python3.4 with stdlib SSL doesn't support ALPN, but supports NPN, which is not supported by APNS.

So our options are:

• Drop Python3.4 support
• For Python3.4 require PyOpenSSL and hyper and use compaibility wrapper from hyper https://github.com/Lukasa/hyper/blob/development/hyper/ssl_compat.py

I drop it for now, and create issue for returning python3.4 support

[coveralls]

Coverage increased (+6.5%) to 91.716% when pulling aab9710 on mock_server_test into 9490736 on develop.

[coveralls]

Coverage increased (+6.5%) to 91.716% when pulling 19e7cc2 on mock_server_test into 9490736 on develop.