xfs_scrub: move failmap and other outputs into read_verify_pool

xfs_scrub: move failmap and other outputs into read_verify_pool

Remove all the indirect verify IO error function calls and whatnot by
making the read_verify_pool track the ranges of failed media and other
problems.  Add some new helper functions that report on the outcome of
the read verifciation so that phase6 can report on what happened.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>