Catch exceptions
This catches 2 different exceptions.
The first one when a received DNS message is malformed.
In this case we need to verify that the HTTP returned code is not in the range 400 <= rcode < 500
resulting in a failing test.
The other one when pyOpenSSL raises an exception.
Here we just display the reasons stored in OpenSSL.SSL.Error.
As expressed in #16 (closed) it would be nice to have better messages, but we rely on the returned error from pyOpenSSL which are just the value given by the OpenSSL library.