Add ability to skip chef registration

This change allows a user to skip the bootstrap stage for a machine.

builtin/provisioners/chef/resource_provisioner.go

@@ -104,6 +104,7 @@ type Provisioner struct {
 	SecretKey             string   `mapstructure:"secret_key"`
 	ServerURL             string   `mapstructure:"server_url"`
 	SkipInstall           bool     `mapstructure:"skip_install"`
+	SkipRegister          bool     `mapstructure:"skip_register"`
 	SSLVerifyMode         string   `mapstructure:"ssl_verify_mode"`
 	UserName              string   `mapstructure:"user_name"`
 	UserKey               string   `mapstructure:"user_key"`
@@ -213,16 +214,18 @@ func (r *ResourceProvisioner) Apply(
 		return err
 	}
 
-	if p.FetchChefCertificates {
-		o.Output("Fetch Chef certificates...")
-		if err := p.fetchChefCertificates(o, comm); err != nil {
-			return err
+	if !p.SkipRegister {
+		if p.FetchChefCertificates {
+			o.Output("Fetch Chef certificates...")
+			if err := p.fetchChefCertificates(o, comm); err != nil {
+				return err
+			}
 		}
-	}
 
-	o.Output("Generate the private key...")
-	if err := p.generateClientKey(o, comm); err != nil {
-		return err
+		o.Output("Generate the private key...")
+		if err := p.generateClientKey(o, comm); err != nil {
+			return err
+		}
 	}
 
 	if p.VaultJSON != "" {

website/source/docs/provisioners/chef.html.markdown

@@ -115,13 +115,17 @@ The following arguments are supported:
   machine. This assumes Chef Client is already installed when you run the `chef`
   provisioner.
 
+* `skip_register (boolean)` - (Optional) Skip the registration of Chef Client on the remote
+  machine. This assumes Chef Client is already registered when you run the `chef`
+  provisioner.
+
 * `ssl_verify_mode (string)` - (Optional) Use to set the verify mode for Chef Client HTTPS
   requests.
 
 * `user_name (string)` - (Required) The name of an existing Chef user to use for registering
   the new Chef Client and (optionally) configure Chef Vaults.
 
-* `user_key (string)` - (Required) The contents of the user key that will be used to 
+* `user_key (string)` - (Required) The contents of the user key that will be used to
   authenticate with the Chef Server. This can be loaded from a file on disk using the [`file()`
   interpolation function](/docs/configuration/interpolation.html#file_path_).