skip NPN tests if NPN is not available (#822)

* skip NPN tests if NPN is not available

* use the right name

Author: reaperhulk

tests/test_ssl.py

@@ -1737,6 +1737,9 @@ def servername(conn):
         assert args == [(server, b"foo1.example.com")]
 
 
+@pytest.mark.skipif(
+    not _lib.Cryptography_HAS_NEXTPROTONEG, reason="NPN is not available"
+)
 class TestNextProtoNegotiation(object):
     """
     Test for Next Protocol Negotiation in PyOpenSSL.