Currently ramdisk and fileio always perform PI verification
before and after backend IO. This approach is not very flexible.
Because some one may want to postpone this work to other layers in
IO stack. For example if we want to test blk_integrity_profile

testcase:
https://github.com/dmonakhov/xfstests/commit/dee408c868861d6b6871dbb3381facee7effdbe4Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>