Report the heat engines under horizon system information panel

Summary
=======
Under Admin->System-> System Information panel (/admin/info/), add new tab 'Orchestration engines' to report heat-engine health details.

Motivation
========
To help admin for monitoring the Orchestration engines status from horizon.

Description
===========
In Kilo-2, Heat is enabled to report the health status of heat-engines. This is similar to how nova, cinder and neutron reports their back-end components.
Currently Horizon reports the health status for nova,cinder and neutron. This blueprint is submitted to enable the same for heat. So under Admin->System-> System Information panel (/admin/info/), new tab 'Orchestration engines' will be added next to the 'Network agents' tab and 'Table' will be added for reporting the heat-engines details.

UX
===
Panel should match the command output of "heat service-list"
+----------+-------------+--------------------------------------+---------+--------+----------------------------+--------+
| hostname | binary | engine_id | host | topic | updated_at | status |
+----------+-------------+--------------------------------------+---------+--------+----------------------------+--------+
| mrkanag | heat-engine | ee5f55ac-defc-4456-acbc-64ff83db8d70 | mrkanag | engine | 2015-02-10T03:28:15.000000 | up |
+----------+-------------+--------------------------------------+---------+--------+----------------------------+--------+

And new horizon table will be as follows :

+----------+-------------+--------------------------------------+---------+--------+----------------------------+--------+
| Hostname | Binary | Engine_id | Host | Topic | Last updated_at | Status |
+----------+-------------+--------------------------------------+---------+--------+----------------------------+--------+
| mrkanag | heat-engine | ee5f55ac-defc-4456-acbc-64ff83db8d70 | mrkanag | engine | 2015-02-10T03:28:15.000000 | up |
+----------+-------------+--------------------------------------+---------+--------+----------------------------+--------+

Testing
======
Horizon should be able to report the information as described in the 'Description' section

Outside Dependencies
==================
Following patches are already merged as part of K-2 & K-3 cycle

Heat : https://review.openstack.org/146044
Python-heatclient: https://review.openstack.org/142727

Requirements Update Required
========================
python-heatclient>=0.3.0 (https://review.openstack.org/142727)

Doc Impact
=========
update the 'Admin user guide' with new tab 'Orchestration engines' under the following sections
OpenStack dashboard—Admin tab (page no 12)
View services information (page no 33)