MB-9745: allow xdcr to recover faster

supervisor2 is built in a way that keeps delaying restart (every time
by configured interfal) until restart can be "fit" into MaxR/MaxT
params of supervisor. With previous settings that only allowed 2
restarts per second.

New code bumps average rate a bit to 5 restarts per second (we might
want to experiment with more), and makes "window" over which restarts
are counted wider.

With our typically large restart intervals (30 seconds) that should
allow more restarts in batch. I.e. if a bunch of vbucket replicators
all failed at about same time, they would be attempted for restart at
about same time. And with larger batch we will be able to allow more
restarts before delaying rest of the "pack" again.

Change-Id: Ia0e5547588958ce9a7fa70f0bae10156deab8610
Reviewed-on: http://review.couchbase.org/31761
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>