tests: filter out TLS distinguished name in certificate checks

tests: filter out TLS distinguished name in certificate checks

The version of GNUTLS in Fedora 34 has changed the order in which encodes
fields when generating new TLS certificates. This in turn changes the
order seen when querying the distinguished name. This ultimately breaks
the expected output in the NBD TLS iotests. We don't need to be
comparing the exact distinguished name text for the purpose of the test
though, so it is fine to filter it out.

Reported-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210804180330.3469683-1-berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>