Use an array to store the pod IDs and use that to build the pod array with consistent ordering,
instead of map ordering, which is random and causes test flakes.
Here are a list of changes along with an explanation of how they work:
1. Add a new string field called TargetSelector to the external version of
extensions Scale type (extensions/v1beta1.Scale). This is a serialized
version of either the map-based selector (in case of ReplicationControllers)
or the unversioned.LabelSelector struct (in case of Deployments and
ReplicaSets).
2. Change the selector field in the internal Scale type (extensions.Scale) to
unversioned.LabelSelector.
3. Add conversion functions to convert from two external selector fields to a
single internal selector field. The rules for conversion are as follows:
i. If the target resource that this scale targets supports LabelSelector
(Deployments and ReplicaSets), then serialize the LabelSelector and
store the string in the TargetSelector field in the external version
and leave the map-based Selector field as nil.
ii. If the target resource only supports a map-based selector
(ReplicationControllers), then still serialize that selector and
store the serialized string in the TargetSelector field. Also,
set the the Selector map field in the external Scale type.
iii. When converting from external to internal version, parse the
TargetSelector string into LabelSelector struct if the string isn't
empty. If it is empty, then check if the Selector map is set and just
assign that map to the MatchLabels component of the LabelSelector.
iv. When converting from internal to external version, serialize the
LabelSelector and store it in the TargetSelector field. If only
the MatchLabel component is set, then also copy that value to
the Selector map field in the external version.
4. HPA now just converts the LabelSelector field to a Selector interface
type to list the pods.
5. Scale Get and Update etcd methods for Deployments and ReplicaSets now
return extensions.Scale instead of autoscaling.Scale.
6. Consequently, SubresourceGroupVersion override and is "autoscaling"
enabled check is now removed from pkg/master/master.go
7. Other small changes to labels package, fuzzer and LabelSelector
helpers to piece this all together.
8. Add unit tests to HPA targeting Deployments and ReplicaSets.
9. Add an e2e test to HPA targeting ReplicaSets.
