Do not land /boot on NVMe disks

[OpenStack Infra]

https://review.openstack.org/205193
commit 355c08a04917f047b88f66242767049d2b1d0ff0
Author: Alexander Gordeev <email address hidden>
Date: Thu Jul 23 20:21:46 2015 +0300

    Do not land /boot on NVMe disks

    There's no point to place /boot partition on NVMe disk
    as grub2 without UEFI support is unable to recognize it and
    read any data from it.

    Unfortunately, fuel-agent doesn't work with grub2-efi.
    It always installs BIOS version of grub2.

    It's just a work around that will allow to land /boot partition
    on non-NVMe disk.

    The absence of non-NVMe disks on a node will cause a failure of
    provisioning.

    DocImpact

    Change-Id: I166c94416ccb152ccd8d1dc780dfb21a774a4f1d
    Co-Authored-By: Atze de Vries <email address hidden>
    Related-Bug: #1474970

[Alexander Gordeev (a-gordeev)]

forwarding to fuel-docs team as the bug is about documentation impact. Please take a look.