Check for optional build_id parameter in rest api.
Check for optional build_id parameter in rest api.

When creating a new target image, you can now specify:
1) an existing image_id (factory creates a new build)
2) an existing build_id
3) an existing build_id and the image_id it belongs to
4) neither (in this case factory will create an image and new build)

LalatenduMohanty/imagefactory,jmcabandara/imagefactory,henrysher/imagefactory,redhat-imaging/imagefactory,jmcabandara/imagefactory,LalatenduMohanty/imagefactory,henrysher/imagefactory,redhat-imaging/imagefactory