perf: reduce number of nodes deep copied

[ryan-mist]

Fixes #N/A

Description

• decreases number of expensive DeepCopy operations in disruption and metrics controllers

How was this change tested?

• make presubmit

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[coveralls]

Pull Request Test Coverage Report for Build 17844334024

Details

• 15 of 15 (100.0%) changed or added relevant lines in 3 files are covered.
• 4 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 81.567%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/controllers/disruption/consolidation.go	4	88.0%

Totals
Change from base Build 17843692914:	-0.02%
Covered Lines:	11465
Relevant Lines:	14056

---

💛 - Coveralls

[jmdeal]

Rather than adding another custom iteration call, does it make more sense to build up the list this way:

var nodes []*state.Node
for node := range cluster.Nodes() {
  if predicate(node) {
    nodes = append(nodes, node.DeepCopy())
  }
}

IMO it's a good idea to minimize the surface of each object and just compose on top of it.