Extra scripts with DevStack support

DevStack project don't merge support of stackforge projects into master.
There is an alternative support to use the devstack infrastructure. The
mechanism based on ability of implementing hooks such as extras.d.

Implemented functionality of the Rally library:
* Install Rally from repository
* Configure Rally and create database tables
* Create a special tenant
* Optionally add devstack installation as a deployment

blueprint rally-devstack-extras

Change-Id: I43b74db203ca385d321ba9d6f79c2bd21f947e13
Merge "Extra scripts with DevStack support"