Support last modified on listing containers

[OpenStack Infra]

https://review.openstack.org/198634
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commit 652276fea60089c8f62cf9495dc873b932652487
Author: Kota Tsuyuzaki <email address hidden>
Date: Mon Dec 15 20:45:41 2014 -0800

    Support last modified on listing containers

    For now, last modified timestamp is supported only on
    object listing. (i.e. GET container)

    For example:

    GET container with json format results in like as:

    [{"hash": "d41d8cd98f00b204e9800998ecf8427e", "last_modified":
    "2015-06-10T04:58:23.460230", "bytes": 0, "name": "object",
    "content_type": "application/octet-stream"}]

    However, container listing (i.e. GET account) shows just a dict
    consists of ("name", "bytes", "name") for each container.

    For example:

    GET accounts with json format result in like as:

    [{"count": 0, "bytes": 0, "name": "container"}]

    This patch is for supporting last_modified key in the container
    listing results as well as object listing like as:

    [{"count": 0, "bytes": 0, "name": "container", "last_modified":
    "2015-06-10T04:58:23.460230"}]

    This patch is changing just output for listing. The original
    timestamp to show the last modified is already in container table
    of account.db as a "put_timestamp" column.

    Note that this patch *DOESN'T* change the put_timestamp semantics.
    i.e. the last_modified timestamp will be changed only at both PUT
    container and POST container.
    (PUT object doesn't affect the timestamp)

    Note that the tuple format of returning value from
    swift.account.backend.AccountBroker.list_containers is now
    (name, object_count, bytes_used, put_timestamp, 0)

    * put_timestamp is added *

    Original discussion was in working session at Vancouver Summit.
    Etherpads are around here:

    https://etherpad.openstack.org/p/liberty-swift-contributors-meetup
    https://etherpad.openstack.org/p/liberty-container-listing-update

    DocImpact

    Change-Id: Iba0503916f1481a20c59ae9136436f40183e4c5b