Add objects for images

part of blueprint lang-pack
Change-Id: If6166243b9d6e1cb1594024a835c725cd6f7b465
Add an image builder api

This is a totally seperate endpoint so it can be deployed seperately
and we can abstract the implemention well away from the rest of
solum. Also this could be used seperatly from solum to simply
build images (once the implementation matures).

part of blueprint lang-pack
Change-Id: I42fc352e787e2d98f933016c0da7fd2f18fe262e