Remove unecessary prep tasks

test/integration/roles/prepare_rax_tests/tasks/main.yml

----
-- name: Check for required variables
-  assert:
-    that:
-      - resource_prefix is defined and resource_prefix
-      - rackspace_username is defined and rackspace_username
-      - rackspace_api_key is defined and rackspace_api_key
-      - rackspace_region is defined and rackspace_region
-      - rackspace_image_human_id is defined and rackspace_image_human_id
-      - rackspace_image_id is defined and rackspace_image_id
-      - rackspace_image_name is defined and rackspace_image_name