Fix for scaling split allocated GameServerSets

[markmandel]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug

/kind cleanup
/kind documentation
/kind feature
/kind hotfix
/kind release

What this PR does / Why we need it:

Fixes bug wherein if a set of Allocations occurred across two or more GameServerSets that had yet to be deleted for a RollingUpdate (because of Allocated GameServers), and a scale down operation moved the Fleet replica count to below the current number of Allocated GameServers -- scaling back up would not move above the current number of Allocated GameServers.

Or to put it another way, the current Fleet update logic didn't consider old GameServerSets with Allocated GameServers but a 0 value for Spec.Replicas as a complete rollout when scaling back up, so the logic went back into rolling update logic, and it all went sideways.

This short circuits that scenario up front.

Which issue(s) this PR fixes:

Close #3287

Special notes for your reviewer:

Found a weird Unit Test in there while I was at it. Fixed it.

[agones-bot]

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[markmandel]

Weird errors on 1.27 generic, in and around:

agones.dev/agones/test/e2e/allocator.TestAllocatorAfterDeleteReplica.func2()
	/go/src/agones.dev/agones/test/e2e/allocator/pod_termination_test.go:98

Going to rerun and see if it's consistent.

[agones-bot]

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[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: gongmax, markmandel

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[google-oss-prow]

New changes are detected. LGTM label has been removed.

[agones-bot]

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[markmandel]

It's still the:

--- FAIL: TestAllocatorAllocateOnGameServerUpdateError (6.53s)
    allocator_test.go:508: 
        	Error Trace:	/go/src/agones.dev/agones/pkg/gameserverallocations/allocator_test.go:508
        	Error:      	Expected nil, but got: &v1.GameServerAllocation{TypeMeta:v1.TypeMeta{Kind:"", APIVersion:""}, ObjectMeta:v1.ObjectMeta{Name:"gsa-1", GenerateName:"", Namespace:"default", SelfLink:"", UID:"", ResourceVersion:"", Generation:0, CreationTimestamp:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), DeletionTimestamp:<nil>, DeletionGracePeriodSeconds:(*int64)(nil), Labels:map[string]string(nil), Annotations:map[string]string(nil), OwnerReferences:[]v1.OwnerReference(nil), Finalizers:[]string(nil), ManagedFields:[]v1.ManagedFieldsEntry(nil)}, Spec:v1.GameServerAllocationSpec{MultiClusterSetting:v1.MultiClusterSetting{Enabled:false, PolicySelector:v1.LabelSelector{MatchLabels:map[string]string(nil), MatchExpressions:[]v1.LabelSelectorRequirement(nil)}}, Required:v1.GameServerSelector{LabelSelector:v1.LabelSelector{MatchLabels:map[string]string(nil), MatchExpressions:[]v1.LabelSelectorRequirement(nil)}, GameServerState:(*v1.GameServerState)(0xc0019222c0), Players:(*v1.PlayerSelector)(nil), Counters:map[string]v1.CounterSelector(nil), Lists:map[string]v1.ListSelector(nil)}, Preferred:[]v1.GameServerSelector(nil), Priorities:[]v1.Priority(nil), Selectors:[]v1.GameServerSelector{v1.GameServerSelector{LabelSelector:v1.LabelSelector{MatchLabels:map[string]string(nil), MatchExpressions:[]v1.LabelSelectorRequirement(nil)}, GameServerState:(*v1.GameServerState)(0xc0019222d0), Players:(*v1.PlayerSelector)(nil), Counters:map[string]v1.CounterSelector(nil), Lists:map[string]v1.ListSelector(nil)}}, Scheduling:"Packed", MetaPatch:v1.MetaPatch{Labels:map[string]string(nil), Annotations:map[string]string(nil)}, Counters:map[string]v1.CounterAction(nil), Lists:map[string]v1.ListAction(nil)}, Status:v1.GameServerAllocationStatus{State:"UnAllocated", GameServerName:"", Ports:[]v1.GameServerStatusPort(nil), Address:"", NodeName:"", Source:"", Metadata:(*v1.GameServerMetadata)(nil)}}
        	Test:       	TestAllocatorAllocateOnGameServerUpdateError

I think I'm going to lose the plot here.

[agones-bot]

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[agones-bot]

Build Succeeded 👏

Build Id: 5bfc0b1d-09e7-46e1-9c42-cd584ebe2575

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.34.0-dev-ea1b999-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.34.0-dev-ea1b999-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.34.0-dev-ea1b999-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.34.0-dev-ea1b999-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.34.0-dev-ea1b999-amd64
• Linux C++ SDK (build): agonessdk-1.34.0-dev-ea1b999-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.34.0-dev-ea1b999-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://ea1b999-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3292/head:pr_3292 && git checkout pr_3292
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.34.0-dev-ea1b999-amd64