the initial calculations for the historical values of comp_at_rest
were wrong. because our historical data only included total amounts
as well as compensation for bandwidth, the at rest value was
calculated as
at_rest = total - bandwidth
unfortunately, that calculation did not take surge pricing into
account correctly. the at rest and bandwidth values do not
include surge pricing, but the total that was used did. so what
we actually calculated was
no_surge_at_rest = surge_total - no_surge_bandwidth
which will create a value that is too large. this migration
fixes the calculation for imports that are old enough and
of a non-negligable difference.
Change-Id: I61eb0b670510f6d7fb8fc3de39ba79150fac10eb
