Nailgun Fixes for smart configuration changes support

https://review.openstack.org/304598
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.

commit 5b2607ab8f371e3479775f09e6ebc8915813ab17
Author: Vladimir Kuklin <email address hidden>
Date: Tue Apr 12 16:05:26 2016 +0300

    Nailgun Fixes for smart configuration changes support

    Simply unhardcode the handler for $.configuration namespace
    to allow a user to modify anything he wants in this namespace.
    The list of modifyable sections on '$.configuration' namespace of astute.yaml
    should not be hardcoded - this makes no sense as support of these pieces
    is implemented on fuel library and plugins side. Hardcoding the list
    will make it impossible for a plugin developer to reuse configuration
    changes feature to support configuration options for plugin.

    DocImpact

    Partial-bug: #1580522

    Change-Id: I4eb18461c0a4f337b649abfcd099259965290ff5