Comment 7 for bug 1640014

Reviewed: https://review.openstack.org/426740
Committed: https://git.openstack.org/cgit/openstack/fuel-astute/commit/?id=9edd8a95767f5cf36e151aaf487405d7e66c4512
Submitter: Jenkins
Branch: stable/8.0

commit 9edd8a95767f5cf36e151aaf487405d7e66c4512
Author: Dmitry Guryanov <email address hidden>
Date: Fri Mar 25 16:19:29 2016 +0300

    Erase only boot code in MBR during node delete

    Zeroing first 1Mb of a block device will almost always
    lead to serios system error, if there is a filesystem
    on this block device and this filesystem is mounted.

    This code had 2 points: to prevent system from booting
    from hard drive after reboot and to prevent anaconda
    (or other OS installer) to automatically recognize
    disk structure. But since we only use image-based provision
    this is not the case anymore.

    It's enough to clear first 446 bytes of MBR where the first
    stage of a bootloader resides. So we will also be able to
    check nodes disks and filesystems after deleting it from
    cluster for troubleshooting for example, because partition
    scheme will not be touched.

    https://wiki.archlinux.org/index.php/Master_Boot_Record

    Change-Id: I60f2b250d6d5997b4b471c27ed00d057ae73c30a
    Fixes-bug: #1538587
    Fixes-bug: #1640014
    (cherry picked from commit e770d4ec7d302e958ffae8db87e633e9d5e3db91)