Increase default and minimum polling intervals.

Increase DEFAULT_FACILITATOR_POLL_INTERVAL to 3600 seconds and increase
MIN_FACILITATOR_POLL_INTERVAL to 10 seconds.
Make facilitator_poll_interval option override other settings.

If the facilitator_poll_interval option is provided, and is a valid
value, it overrides the facilitator-provided interval and the default
interval. If the option is missing, fall back on the facilitator
interval, and absent that, the default interval. If any value is smaller
than MIN_FACILITATOR_POLL_INTERVAL, that is used instead.
Do not fail if facilitator doesn't provide a polling interval.

Do not raise an exception in get_reg() if the facilitator doesn't
provide a polling interval.