Add security group deletion to the cleanup util

Add security group deletion code to the stress cleanup utility.

Change-Id: I39b70da4000da1a72fff7b3384831673eb7e06f7
Stop leaking test_update_images

test_update_images create a image but doesn't delete it.
This commit fixes it.

Partially Implements: blueprint stop-leaking

Change-Id: Iaee04312ff7aa59cbba8fea30874ccd3993219f7
Merge "Stop leaking test_update_images"
Merge "Add security group deletion to the cleanup util"