If failed_to_recv is set, consensus can be empty

If failed_to_recv is set (node detect itself not able to receive
message), we can end up with assert, because my_failed_list and
my_member_list are same list. This is happening because we are not
following specification and we allow to mark node itself as failed.
Because if failed_to_recv is set and we reached consensus across nodes,
single node membership is created (ignoring both fail list and
member_list), we can skip assert.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>