Added methods for patching deployment info per object

[OpenStack Infra]

https://review.openstack.org/342880
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.

commit 5167527dc442b81aeca56da2af96c7f1c835d993
Author: Bulat Gaifullin <email address hidden>
Date: Wed Jul 13 20:09:39 2016 +0300

    Added methods for patching deployment info per object

    Instead of wide callbacks process_deployment or process_provision
    implemented methods to patch deployemnt or provision info per
    cluster or node.
    The code of extensions and tests was updated accordingly.
    Also added helper to mark methods of extension as deprecated.
    the extension load behaviour was modified, instead of fail operation
    when extension cannot be loaded, the nailgun only write error in log
    that extension is not loaded and continue operation.

    Partial-Bug: 1596987
    Change-Id: I577c8ffc105734e12646ca7c6a4fe4927e70b119
    DocImpact