Evacuate instance to a scheduled host

[OpenStack Infra]

https://review.openstack.org/38198
commit 679b8220a83c82f02475075488b9a0cc0168709d
Author: Anuj Mathur <email address hidden>
Date: Wed Mar 20 13:58:07 2013 +0530

    Evacuate instance to a scheduled host

    In the event of a unrecoverable hardware failure, support needs to
    relocate an instance to another compute so it can be rebuilt. This
    API call locates a suitable host within the same
    cell (using nova-scheduler), and performs an update of the
    instance's location to the new host (similar to a rebuild). This
    call is only available to users with the Admin role.

    Compute api calls the conductor. conductor used scheduler to select
    destination.
    DocImpact

    Change-Id: Idb0869c1b7571be0cc136e6588aeffc61d987ab7
    Implements: blueprint find-host-and-evacuate-instance