Fixing bug with session logging shared ciphers

This change fixes a bug with the KmipSession logging shared
ciphers used by the TLS connection. The SSLSocket only supports
shared cipher information starting with Python 3.5. Any use of
the server with older versions of Python will fail when any
connection attempts are made. This fix adds a conditional check
that skips logging shared cipher information if the SSLSocket
does not support that information.

Fixes #361

kmip/services/server/session.py

@@ -158,6 +158,7 @@ class KmipSession(threading.Thread):
         max_size = self._max_response_size
 
         try:
+            if hasattr(self._connection, 'shared_ciphers'):
                 shared_ciphers = self._connection.shared_ciphers()
                 self._logger.debug(
                     "Possible session ciphers: {0}".format(len(shared_ciphers))