Update x509.load_certificate and related functions to return
python-cryptography ``Certificate`` objects. Update the call sites
accordingly, including removal of NSS initialisation code.
Also update GeneralName parsing code to return python-cryptography
GeneralName values, for consistency with other code that processes
GeneralNames. The new function, `get_san_general_names`, and
associated helper functions, can be removed when python-cryptography
provides a way to deal with unrecognised critical extensions.
Part of: https://fedorahosted.org/freeipa/ticket/6398
Reviewed-By: Jan Cholasta <jcholast@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
Fraser Tweedale
db116f73fe