Previously if we fail to connect to CHAOS during a scrape no metrics are
emitted.
Now a aaisp_scrape_success metric is always emitted with values 0 for
failure and 1 for success, along the lines of blackbox_exporter's
probe_success metric.
The README for the Prometheus exporter failed to mention that you must
set some environment variables for authentication or that you can change
the address the exporter listens on.