'group_range_count' doesn't properly consider the pair-wise range
structure. It may split the ranges into wrong pairs if it evaluates to
an odd number.
For example, for an input range string of "6,0,2,10,12,20,22" with 4
threads, group_range_count becomes 1. It would then try to verify (0,2),
(2,10), (10,12) and (12,20). Note that (2,10) and (12,20) are not valid
ranges to be verified, and with (20,22) uncovered.
Bug: 68343761
Test: Trigger update_verifier verification. Check the number of verified
blocks against the one in care_map.txt.
Change-Id: I7c5769325d9866be06c45e7dbcc0c8ea266de714
6ec94c023e