Add support for headnode base-image selection

The deployment tests now require TWO base-images, named base-headnode and
base-headnode-2
Merge branch 'devel' into multiple-base-imgs
Merge pull request #294 from gsilvis/multiple-base-imgs

Add support for headnode base-image selection
Merge branch 'devel' into headnode_img_query

Conflicts:
	haas/test_common.py