Use 3.4's ssl.create_default_context when available

Related #472 
So:

```python

    def set_ciphers(self, cipher_suite):
        self.ciphers = cipher_suite

    def wrap_socket(self, socket, server_hostname=None):
        kwargs = {...}
        if sys.version_info[:2] == (2, 7):
            kwargs["ciphers"] = self.ciphers
        return wrap_socket(socket, **kwargs)
```