Merge pull request #43271 from liggitt/affinity-namespace

Automatic merge from submit-queue (batch tested with PRs 43313, 43257, 43271, 43307)

Remove 'all namespaces' meaning of empty list in PodAffinityTerm

Removes the distinction between `null` and `[]` for the PodAffinityTerm#namespaces field (option 4 discussed in https://github.com/kubernetes/kubernetes/issues/43203#issuecomment-287237992), since we can't distinguish between them in protobuf (and it's a less than ideal API)

Leaves the door open to reintroducing "all namespaces" function via a dedicated field or a dedicated token in the list of namespaces

Wanted to get a PR open and tests green in case we went with this option.

Not sure what doc/release-note is needed if the "all namespaces" function is not present in 1.6

pkg/generated/openapi/zz_generated.openapi.go

@@ -5925,7 +5925,7 @@ func GetOpenAPIDefinitions(ref openapi.ReferenceCallback) map[string]openapi.Ope
 						},
 						"namespaces": {
 							SchemaProps: spec.SchemaProps{
-								Description: "namespaces specifies which namespaces the labelSelector applies to (matches against); nil list means \"this pod's namespace,\" empty list means \"all namespaces\" The json tag here is not \"omitempty\" since we need to distinguish nil and empty. See https://golang.org/pkg/encoding/json/#Marshal for more details.",
+								Description: "namespaces specifies which namespaces the labelSelector applies to (matches against); null or empty list means \"this pod's namespace\"",
 								Type:        []string{"array"},
 								Items: &spec.SchemaOrArray{
 									Schema: &spec.Schema{
@@ -5945,7 +5945,6 @@ func GetOpenAPIDefinitions(ref openapi.ReferenceCallback) map[string]openapi.Ope
 							},
 						},
 					},
-					Required: []string{"namespaces"},
 				},
 			},
 			Dependencies: []string{