Initial implementation of HEAT CFN client and Template registration

This patch adds support for connecting to Heat using:

from tuskar.heat.client import HeatClient as heat_client

heat_client().method

Also update the #index action in DataCenter controller to support
template validation and registration.
Added 'boto' to list of requirements
Add ResourceClass to session when updating Racks
Fix updating the Rack when ResourceClass is already assigned (#39)
Merge pull request #40 from mfojtik/rack_rs_id

Ignore updating of ResourceClass when it is already assigned to Rack (#39)
Create example datacenter.

This changes the sample_data to describe an example datacenter, allowing for use
in provisioning via HEAT once that piece of integration is comeplte.
Add checklist to CONTRIBUTING.
Merge pull request #42 from jguiditta/docs

Add checklist to CONTRIBUTING.
Merge pull request #36 from mfojtik/heat

Initial implementation of HEAT CFN client and Template registration
Merge pull request #41 from jguiditta/sample_data_center

Datacenter description