Pretty print all JSON responses from REST API

[Jim Baker]

For better demo/human usage of the REST API, and to follow fairly common practice, we should always pretty print the JSON responses. This adds negligible overhead: the JSON encoder in the json library has virtually no overhead for adding indentation; and gzip encoding would take care of this and other JSON encoding overhead issues in terms of resulting size.

This should be a few line fix, per http://flask-restful-cn.readthedocs.io/en/0.3.5/extending.html#content-negotiation

For the specific pretty printing, I suggest we use {"indent": 2, "sort_keys": True} (such sorting is also negligible in cost, especially given pagination).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/442588

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/442588
Committed: https://git.openstack.org/cgit/openstack/craton/commit/?id=0f7ee6d79189b2d8c5a81cf9e9598f96575f511d
Submitter: Jenkins
Branch: master

commit 0f7ee6d79189b2d8c5a81cf9e9598f96575f511d
Author: git-harry <email address hidden>
Date: Tue Mar 7 15:33:08 2017 +0000

    Pretty-print format all JSON response bodies

    Flask-RESTful automatically converts a response body to JSON when it
    creates the Response object. The Flask app configuration option
    RESTFUL_JSON is added by this commit to appropriately modify how the
    JSON body is constructed.

    response_filter has been modified so that it returns a tuple of
    information that Flask-RESTful will use to create an appropriately
    formatted response.

    Resource.error_response is creating the Response object itself and so
    has been modified to format the JSON in the same way as Flask-RESTful.
    Ideally, error_response would not create a separate Response object
    however addressing this is a separate issue.

    Change-Id: I02eafaf48d7c6e2ceab0add2f78cf6aa1b890f18
    Closes-bug: 1664328