pkg/adt: merge etcd master & fix interval tree

[xkeyideal]

Please read https://github.com/etcd-io/etcd/blob/master/CONTRIBUTING.md#contribution-flow.

[gyuho]

@xkeyideal Could you rebase your branch from current master, and cherry-pick your patch? It makes code review much easier. Thanks!

[gyuho]

Also please squash all your commits into one, without merge commit.

[codecov-io]

Codecov Report

Merging #10977 into master will decrease coverage by 0.43%.
The diff coverage is 87.2%.

@@            Coverage Diff             @@
##           master   #10977      +/-   ##
==========================================
- Coverage   64.22%   63.78%   -0.44%     
==========================================
  Files         401      401              
  Lines       37540    37541       +1     
==========================================
- Hits        24110    23946     -164     
- Misses      11808    11986     +178     
+ Partials     1622     1609      -13

Impacted Files	Coverage Δ
pkg/adt/interval_tree.go	86.59% <87.2%> (+1.84%)	⬆️
client/keys.go	68.34% <0%> (-23.12%)	⬇️
auth/store.go	45.08% <0%> (-21.08%)	⬇️
clientv3/naming/grpc.go	59.64% <0%> (-15.79%)	⬇️
pkg/netutil/netutil.go	63.11% <0%> (-5.74%)	⬇️
etcdserver/api/v3election/election.go	61.11% <0%> (-2.78%)	⬇️
etcdserver/api/v3rpc/watch.go	78.43% <0%> (-1.64%)	⬇️
pkg/schedule/schedule.go	81.69% <0%> (-1.41%)	⬇️
etcdserver/api/v2http/client.go	84.3% <0%> (-1.21%)	⬇️
... and 20 more

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[gyuho]

Also change this line to Fatalf to validate the fix.

etcd/pkg/adt/interval_tree_test.go

Lines 282 to 301 in 9a2af73

	if !reflect.DeepEqual(expectedAfterDelete11, visitsAfterDelete11) {
	// "black-height" property is violated here
	//
	// TODO: fix this
	// [510,511]
	// / \
	// ---------- --------------------------
	// / \
	// [82,83] [830,831]
	// \ / \
	// \ / \
	// [383,384] [647,648] [899,900]
	// / \ \ / \
	// / \ \ / \
	// [261,262] [410,411] [815,816] [888,889] [972,973]
	// / \ /
	// / \ /
	// [238,239] [292,293] [953,954]
	//
	t.Logf("level order after deleting '11' expected %v, got %v", expectedAfterDelete11, visitsAfterDelete11)

[xkeyideal]

@xkeyideal #10978