Phased updater and weekends

[Julian Andres Klode]

After some quick chat, I'd like to propose that we extend the
policy to not release SRUs from Fri-Sun to the phased updates
and not phase them to a 100% at those times.

Cautious users configure their systems to not install phased updates,
so they will only see new updates once they reach 100% and that
happening on weekends is not particularly helpful.

I propose that essentially when the phased-updater is started
between

    Friday 00:00 UTC and Monday 12:00 UTC

that it never increments the value to 100.

The second aspect of the weekend question is whether to increment
the phased update percentage at all, that is should people using
the defaults be exposed to new updates over the weekend?

To recall, a phased update is usually installed if

Phased-Update-Percentage > rng(seeded with:
                                name-version-machineId).randint(0,100)


When increasing from 10% to 20%, that means 10% more users will
receive the update such that a total of 20% of machines received
it.

Or default policies are:

- low: 10 points per run (2.5 days to complete)
- medium: 5 points per run (5 days to complete)
- slow: 1 point per run (25 days to complete)

These likely would need adjusting, as we run the phased
updater only for 3.5 instead of 7 days. Particularly, the
slow policy would now take 7 weeks instead of 3.5 (25/7=3.5),
which is too slow, accordingly slow should receive a bump
to receive 2 points per run.

Medium may be worthwhile to increase it a bit, such that it
takes 4 days to complete, this avoids it skipping over 2
weekends (the last released update should be half a day in
the current week + 3.5 days the next week = 4 days).

It may make sense to add an adjustment factor for a weekend
to scale non-linearly after to "catch up". If the update was
phased at 50% over the weekend, that's very different from
an update that was phased at 10% over the weekend and it
could move to 100% faster.
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