common/obj_bencher.cc: make verify error fatal

common/obj_bencher.cc: make verify error fatal

When run without "--no-verify", all verification errors are noted,
but they are not forwarded/reported anywhere else but to cerr, which
will cause automated testing to ignore them. Make seq_read_bench and
rand_read_bench return -EIO on any verification error which will,
in turn, return it back to caller.

Fixes: #14973
Signed-off-by: Piotr Dałek <piotr.dalek@ts.fujitsu.com>
(cherry picked from commit 658bba85c488a38e25bc598637258c263f711631)