Add phase 1 of validation tightening.

https://github.com/kubernetes/enhancements/blob/master/keps/sig-storage/177-volume-snapshot/tighten-validation-webhook-crd.md

1. Ratcheting validation webhook server image
2. Controller labels invalid objects
3. Unit tests for webhook
4. Deployment README and example deployment method with certs
5. Update top-level README

Racheting validation:
1. webhook is strict on create
2. webhook is strict on updates where the existing object passes strict validation
3. webhook is relaxed on updates where the existing object fails strict validation (allows finalizer removal, status update, deletion, etc)

Additionally the validating wehook server will perform immutability
checks on scenario 2 above.

vendor/github.com/spf13/cobra/zsh_completions.md

@@ -0,0 +1,39 @@
+## Generating Zsh Completion for your cobra.Command
+
+Cobra supports native Zsh completion generated from the root `cobra.Command`.
+The generated completion script should be put somewhere in your `$fpath` named
+`_<YOUR COMMAND>`.
+
+### What's Supported
+
+* Completion for all non-hidden subcommands using their `.Short` description.
+* Completion for all non-hidden flags using the following rules:
+  * Filename completion works by marking the flag with `cmd.MarkFlagFilename...`
+    family of commands.
+  * The requirement for argument to the flag is decided by the `.NoOptDefVal`
+    flag value - if it's empty then completion will expect an argument.
+  * Flags of one of the various `*Array` and `*Slice` types supports multiple
+    specifications (with or without argument depending on the specific type).
+* Completion of positional arguments using the following rules:
+  * Argument position for all options below starts at `1`. If argument position
+    `0` is requested it will raise an error.
+  * Use `command.MarkZshCompPositionalArgumentFile` to complete filenames. Glob
+    patterns (e.g. `"*.log"`) are optional - if not specified it will offer to
+    complete all file types.
+  * Use `command.MarkZshCompPositionalArgumentWords` to offer specific words for
+    completion. At least one word is required.
+  * It's possible to specify completion for some arguments and leave some
+    unspecified (e.g. offer words for second argument but nothing for first
+    argument). This will cause no completion for first argument but words
+    completion for second argument.
+  * If no argument completion was specified for 1st argument (but optionally was
+    specified for 2nd) and the command has `ValidArgs` it will be used as
+    completion options for 1st argument.
+  * Argument completions only offered for commands with no subcommands.
+
+### What's not yet Supported
+
+* Custom completion scripts are not supported yet (We should probably create zsh
+  specific one, doesn't make sense to re-use the bash one as the functions will
+  be different).
+* Whatever other feature you're looking for and doesn't exist :)