Inherit base image properties on instance creation

When creating an instance, a few properties from the image will be saved
in the instance's system_metadata under the prefix 'image_' for latter
usage.

The keys that the instance will inherit from the image are: 'min_ram',
'min_disk', 'disk_format' and 'container_format' together with the
inheritable image properties.

Related to bug #1039662

Change-Id: I358fb6d8dcafd67c289fe5083bb82140f3759fee
Merge "Inherit base image properties on instance creation"