pool: Add frost protection

pool: Add frost protection

The motor on the bypass valve probably burned out when it was being moved
during the winter while it was frozen. Just open it up at 5°C and leave
it open regardless of the temperature of the roof sensor.

Also fix the 'pump_default' script to run later at boot after the time
zone has actually been set, or it does the wrong thing.

And fix the "turn pump on if it's above 20°C in the morning" logic to
actually operate between 7:30am and 10am as it promises, instead of only
between 7:30 to 8, and 8 to 9. Oops :)