Add a new "qom-tests" to exercise basic object lifecycle. Instantiate
all non-abstract objects, get and set properties and unref.
This should quickly find leaks and other related issues that are
eventually triggerable at run-time with QMP qom commands.
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>