Add a test with QEMU 2.4.0 capabilites, as well as the latest caps.

The code paths for formatting TLS options will be altered and
2.4.0 is the newest version where QEMU_CAPS_OBJECT_TLS_CREDS_X509
is not supported.
Signed-off-by: NJán Tomko <jtomko@redhat.com>