Adding common base class for Rackspace Resource providers

Change-Id: If7d15e01c53fb6db4bdee5759b0ef4f087640c58

Conflicts:

	heat/engine/resources/rackspace/rackspace_resource.py
	requirements.txt
Bug fix

Change-Id: I04c84dd8ab07b611156c063a738cd16bf7efb316
Refactor FnGetAtt

Change-Id: I8e13cd2827a49bde71123e0122a7e36125dfcff4
Add docstrings.

Change-Id: I66956f9f7c95aa4ec85395fd227179b0fd0edba1