*: let per-replica constraints specify less than all a zone's replicas

[a-robinson]

Release note (cli change): Per-replica constraints no longer have to add
up to the total number of replicas in a range. If don't specify all the
replicas, then the remaining replicas will be allowed on any store.

[cockroach-teamcity]

This change is 

[petermattis]

The complaint about the difficulty in understanding the test cases shouldn't hold up this PR. I did work through what they are testing and they look correct.

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Review status: 0 of 7 files reviewed at latest revision, 1 unresolved discussion, all commit checks successful.

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pkg/storage/allocator_scorer_test.go, line 746 at r1 (raw file):

		},
		{
			name: "multiple required constraints with NumReplicas and sum(NumReplicas) < zone.NumReplicas",

I'm going to reiterate my complaint about these tests. They are quite difficult to review because the context needed to review them is not local. I had to open up allocator_scorer_test.go in an editor and flip back and forth looking at the testStores setup. I don't have a concrete suggestion, only a feeling that something can be improved here.

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Comments from Reviewable

[a-robinson]

Review status: 0 of 7 files reviewed at latest revision, 1 unresolved discussion, all commit checks successful.

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pkg/storage/allocator_scorer_test.go, line 746 at r1 (raw file):

Previously, petermattis (Peter Mattis) wrote…

I'm going to reiterate my complaint about these tests. They are quite difficult to review because the context needed to review them is not local. I had to open up allocator_scorer_test.go in an editor and flip back and forth looking at the testStores setup. I don't have a concrete suggestion, only a feeling that something can be improved here.

I assume some better naming of the stores (in these tests) or using names at all rather than just numbers (in the big rebalance tests) would help.

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Comments from Reviewable