Display resource details based on Host Aggregates

An Admin user should be able to group resources based on host aggregates and display their capacity metrics in graphical/tabular formats, based on those groupings. The support can be provided both on CLI as well as Horizon.

Description
===========

This will enable the Admin to select different host aggregates and show their corresponding capacity metrics (example RAM, CPU, Disk usage etc) as graphs (using Grafana/ any other compatible alternative) and also in downloadble tabular formats.

Proposed Change
===============

The view may look something like - https://drive.google.com/file/d/0B-plFIxVwCV9U2tvUHV1V3JHb3c/view

The breakup of the activities is listed below-
1) Update Horizon Host Aggregates section – make every Host aggregate name linkable to a new page.
2) This new page provides two tables for its host aggregate specific information and Usage details.
3) Host aggregate specific information is pulled from its table in the nova database.
Host aggregate usage details (RAM, CPU, Disk) will be displayed as graph under the usage tab using Grafana/others depending on Kilo compatibility.
4) Host aggregate usage details (RAM, CPU, Disk) will also be a displayed in the usual Horizon tabular format, along with an option to download the table as CSV file.
5) Both CLI and Horizon support will be provided.

Any suggestions will be appreciated.

Advantage
=========

Better visibility to the Admin user to club the resources on the basis of host aggregates.
Provide both CLI and Horizon support.