Get image properties instead of the whole image

When booting an instance using the new BDMv2 API we can specify to boot
from a volume created from an image on the fly. In this case the API
should pass the image properties to the new instance so it can get some
important parameters that it might specify.

After adding the new BDMv2 API in 13180f76, we introduced a mistake in
the method that gets the image properties (from the boot BDM) if no
image_ref is defined. When the source is an image it will return the
whole image metadata instead of getting just the properties. This
causes that when the source image is an AMI the instance won't have the
ramdisk and kernel properties set and will fail to boot.

This patch fixes the image properties when booting from a volume created
from an image.

Fixes bug #1220318

Change-Id: Ibcd60510cc909fcaa0d6d4769f91c070dfaf22ff
Merge "Get image properties instead of the whole image"