Merge pull request #56995 from mtaufen/kc-flags-precedence-redo

Automatic merge from submit-queue (batch tested with PRs 56995, 58498, 57426, 58902, 58863). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

flag precedence redo

Changes the Kubelet configuration flag precedence order so that flags take precedence over config from files/ConfigMaps.

This should fix the re-parse issue with #56097 that led to revert.

Fixes #56171.

In order to prevent global flags (registered in 3rd party libs, etc.) from leaking into the command's help text, this PR turns off Cobra's flag parsing in the `kubelet` command and re-implements help and usage funcs for the Kubelet. Cobra's default funcs automatically merge all global flags into the command's flagset, which results in incorrect help text. I tried to keep the formatting as close as possible to the what the Kubelet currently produces.

Diff between Kubelet's help text on `upstream/master` vs `mtaufen/kc-flags-precedence-redo`, which shows a leaked flag being removed, but no change to the formatting:
```
diff --git a/upstream.master.help b/mtaufen.kc-flags-precedence-redo.help
index 798a030..0797869 100644
--- a/upstream.master.help
+++ b/mtaufen.kc-flags-precedence-redo.help
@@ -30,7 +30,6 @@ Flags:
       --authorization-mode string                                                                                 Authorization mode for Kubelet server. Valid options are AlwaysAllow or Webhook. Webhook mode uses the SubjectAccessReview API to determine authorization. (default "AlwaysAllow")
       --authorization-webhook-cache-authorized-ttl duration                                                       The duration to cache 'authorized' responses from the webhook authorizer. (default 5m0s)
       --authorization-webhook-cache-unauthorized-ttl duration                                                     The duration to cache 'unauthorized' responses from the webhook authorizer. (default 30s)
-      --azure-container-registry-config string                                                                    Path to the file containing Azure container registry configuration information.
       --bootstrap-checkpoint-path string                                                                          <Warning: Alpha feature> Path to to the directory where the checkpoints are stored
       --bootstrap-kubeconfig string                                                                               Path to a kubeconfig file that will be used to get client certificate for kubelet. If the file specified by --kubeconfig does not exist, the bootstrap kubeconfig is used to request a client certificate from the API server. On success, a kubeconfig file referencing the generated client certificate and key is written to the path specified by --kubeconfig. The client certificate and key file will be stored in the directory pointed by --cert-dir.
       --cadvisor-port int32                                                                                       The port of the localhost cAdvisor endpoint (set to 0 to disable) (default 4194)
```

Ultimately, I think we should implement a common lib that K8s components can use to generate clean help text, as the global flag leakage problem affects all core k8s binaries. I would like to do so in a future PR, to keep this PR simple. We could base the help text format on the default values returned from `Command.HelpTemplate` and `Command.UsageTemplate`. Unfortunately, the template funcs used to process these defaults are private to Cobra, so we'd have to re-implement these, or avoid using them.

```release-note
NONE
```

Kubernetes-commit: cf92d921d907f2c3fdf635b690849fd663705638

pkg/util/flag/BUILD

@@ -32,6 +32,7 @@ go_library(
         "map_string_bool.go",
         "map_string_string.go",
         "namedcertkey_flag.go",
+        "noop.go",
         "omitempty.go",
         "string_flag.go",
         "tristate.go",

pkg/util/flag/noop.go

@@ -0,0 +1,41 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package flag
+
+import (
+	goflag "flag"
+	"github.com/spf13/pflag"
+)
+
+// NoOp implements goflag.Value and plfag.Value,
+// but has a noop Set implementation
+type NoOp struct{}
+
+var _ goflag.Value = NoOp{}
+var _ pflag.Value = NoOp{}
+
+func (NoOp) String() string {
+	return ""
+}
+
+func (NoOp) Set(val string) error {
+	return nil
+}
+
+func (NoOp) Type() string {
+	return "NoOp"
+}