Strictly isolate group of hosts for an image

The aim of this blueprint is to improve the filter
`AggregateImagePropertiesIsolation`

An operator wants to schedule instances for a specific image
on a pre-defined group of hosts. In addition, he wants to
strictly isolate this group of hosts for the image only.

blueprint restrict-image-isolation-with-defined-keys
Change-Id: I98ee9a09b694abda0df7ddf8f95cf9e23b162372
Merge "Strictly isolate group of hosts for an image"