The main purpose of that patch is to allow creation of "virtual"
container_skel, that will not generate any containers in inventory,
but will contain all containers of corresponsive hosts. That might be
useful in usecases like AZs, or when deployer simply wants to create
custom groups and include all bare metal hosts along with all
containers on them to the same group. Such behaviour can be triggered
when empty belongs_to is provided for container_skel along with is_nest
property. Then container_skel item will contain host-containers and it's
children.
Change-Id: Ic5570bfe9f0f54d1ea1e067834c11e6c390a2686
fb34651cc2