tests/qemu-iotests/262: Check for availability of "blkverify" first

tests/qemu-iotests/262: Check for availability of "blkverify" first

In downstream RHEL builds, we do not have "blkverify" enabled, so
iotest 262 is currently failing there. Thus let's list "blkverify"
as required item so that the test properly gets skipped instead if
"blkverify" is missing.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230104112850.261480-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>