crypto: use a stronger private key for tests

crypto: use a stronger private key for tests

The unit tests using the x509 crypto functionality have started
failing in Fedora 33 rawhide with a message like

      The certificate uses an insecure algorithm

This is result of Fedora changes to support strong crypto [1]. RSA
with 1024 bit key is viewed as legacy and thus insecure. Generate
a new private key which is 3072 bits long and reasonable future
proof.

[1] https://fedoraproject.org/wiki/Changes/StrongCryptoSettings2

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200715154701.1041325-1-berrange@redhat.com>
Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>