nova: configure file injection by the means of config drive

[OpenStack Infra]

https://review.openstack.org/322434
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.

commit 4418fba67d370cc5be7f40bd77776cde2d69828b
Author: Roman Podoliaka <email address hidden>
Date: Fri May 27 12:35:50 2016 +0300

    nova: configure file injection by the means of config drive

    We've seen a number of problems with qemu-nbd (from files not being
    injected randomly to kernel panics), and while libguestfs is a
    better solution here it does not work out of box on Ubuntu. Neither
    of these can be used for file injection when instance ephemeral
    drives are stored in Ceph.

    Disabling of file injection in Nova libvirt drive allows us to unify
    the settings for Ubuntu vs CentOS and file vs Ceph-based ephemerals.
    In this case file injection can still be performed by the means of
    config drive + cloud-init within images.

    Upstream Nova / Devstack explicitly disabled file injection in favor
    of using config drives in:

    9ce99a44cf85e431227536e2251ef05b52e61524

    and

    I2388ef0df12a6289b619bfaf30cb952fcc48ef41

    DocImpact

    File injection is no longer performed on the compute node because it's
    slow and error-prone. Instead files to be injected are placed on a
    config drive, which is automatically created for every instance. It's up
    to cloud-init or a similar mechanism within the image itself to perform
    injection on instance boot.

    Closes-Bug: #1467860
    Closes-Bug: #1556819
    Related-Bug: #1467579
    Related-Bug: #1493767

    Change-Id: Ie46aa3f48d62b7500a7e326348b35573b3262641