Adds CRUD CLI commands for Resource Class

Adds tests for CRUD operations on Resource Class
Renames test file for resource class to be plural

Implements part of
https://blueprints.launchpad.net/python-tuskarclient/+spec/resource-classes-cli

Change-Id: Ia02ee517f000c5a53d5c69d6f73f8d4c4f80dfac
Adds resource-class-{add,remove}-rack to CLI

Adds tests for resource-class-{add,remove}-rack
Change-Id: I9c872c32e53ec3eea9329f98fdeba82975f3f0c2