style and documentation changes per PR review comments

builder/amazon/ebs/step_stop_instance.go

@@ -26,7 +26,7 @@ func (s *stepStopInstance) Run(state multistep.StateBag) multistep.StepAction {
 
 	var err error
 
-	if s.DisableStopInstance == false {
+	if !s.DisableStopInstance {
 		// Stop the instance so we can create an AMI from it
 		ui.Say("Stopping the source instance...")
 		_, err = ec2conn.StopInstances(&ec2.StopInstancesInput{
@@ -38,6 +38,8 @@ func (s *stepStopInstance) Run(state multistep.StateBag) multistep.StepAction {
 			ui.Error(err.Error())
 			return multistep.ActionHalt
 		}
+	} else {
+		ui.Say("Automatic instance stop disabled. Please stop instance manually.")
 	}
 
 	// Wait for the instance to actual stop

website/source/docs/builders/amazon-ebs.html.md

@@ -116,6 +116,19 @@ builder.
 -   `availability_zone` (string) - Destination availability zone to launch
     instance in. Leave this empty to allow Amazon to auto-assign.
 
+-   `disable_stop_instance` (boolean) - Packer normally stops the build instance
+    after all provisioners have run. For Windows instances, it is sometimes
+    desirable to [run Sysprep](http://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ami-create-standard.html)
+    which will stop the instance for you. If this is set to true, Packer *will not*
+    stop the instance and will wait for you to stop it manually. You can do this
+    with a [windows-shell provisioner](https://www.packer.io/docs/provisioners/windows-shell.html).
+
+    ``` {.javascript}
+    {
+      "type": "windows-shell",
+      "inline": ["\"c:\\Program Files\\Amazon\\Ec2ConfigService\\ec2config.exe\" -sysprep"]
+    }```
+
 -   `ebs_optimized` (boolean) - Mark instance as [EBS
     Optimized](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSOptimized.html).
     Default `false`.