Switch to a custom FlagSet and add a nicer usage message.
Check for the required CHAOS_CONTROL_LOGIN and CHAOS_CONTROL_PASSWORD
environment variables and exit with an error if neither is set. The
usage string also mentions that both must be set.
Create a standard log object and use dependency injection to pass it to
the broadbandCollector and a new loggingMiddleware for wrapping HTTP
requests to log the request.
Logs are emitted as structured JSON logs by default but can be switched
to a human-friendly output by passing -log.level console.
The Prometheus client_golang library has also been upgraded.
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.
