Allow block devices without device_name

[OpenStack Infra]

https://review.openstack.org/40229
commit e65536c865df2285e179a076e195fca820fcf806
Author: Xavier Queralt <email address hidden>
Date: Fri Aug 2 16:42:04 2013 +0200

    Allow block devices without device_name

    This patch removes the check in the API that prevented having block
    devices without 'device_name' and makes the compute manager capable of
    guessing those names.

    Before creating the instance, the manager will check each one of the
    block devices that should be attached and verify that all of them have a
    device_name assigned. If any of them doesn't, it will try to guess a
    valid name using the method `get_next_device_name', which should be
    implemented by the drivers, or by calling the generic method from the
    utils module `get_device_name_for_instance'.

    It also takes care of assigning the correct device name to the root
    device (boot_index=0) to make it agree with the field `root_device_name'
    from the instance.

    DocImpact

    Part of blueprint: improve-block-device-handling

    Change-Id: I84541f8ff6e1b5978734e5def69946d014c66fdf

[Tom Fifield (fifieldt)]

This seems like reasonable/expected behaviour/internal workings that doesn't need separate documentation.