To check affinity and anti-affinity policies for scheduling instances,
we use the RequestSpec.instance_group.hosts field to check the hosts
that have group members on them. Access of the 'hosts' field calls
InstanceGroup.get_hosts during a lazy-load and get_hosts does a query
for all instances that are members of the group and returns their hosts
after removing duplicates. The InstanceList query isn't targeting any
cells, so it will return [] in a multi-cell environment in both the
instance create case and the instance move case. In the move case, we
do have a cell-targeted RequestContext when setup_instance_group is
called *but* the RequestSpec.instance_group object is queried early in
compute/api before we're targeted to a cell, so a call of
RequestSpec.instance_group.get_hosts() will result in [] still, even
for move operations.
This makes setup_instance_group query all cells for instances that are
members of the instance group if the RequestContext is untargeted, else
it queries the targeted cell for the instances.
Closes-Bug: #1746863
Change-Id: Ia5f5a0d75953b1154a8de3e1eaa15f8042e32d77
(cherry picked from commit 14f4c502f9)
3051a0d5d5