Add option to tell packer not to stop the instance

It is sometimes desirable to sysprep a windows machine before creating
an EC2 image. The AWS-approved way to do this is to run
ec2configservice.exe -sysprep and let ec2configservice shut down the instance.
This change adds an option to disable the stop instance call issued by packer
so that the user can control when the machine is stopped.

builder/amazon/common/run_config.go

@@ -23,7 +23,8 @@ type RunConfig struct {
 	SourceAmi                string            `mapstructure:"source_ami"`
 	SpotPrice                string            `mapstructure:"spot_price"`
 	SpotPriceAutoProduct     string            `mapstructure:"spot_price_auto_product"`
-	SecurityGroupId          string            `mapstructure:"security_group_id"`
+  DisableStopInstance      bool              `mapstructure:"disable_stop_instance"`
+  SecurityGroupId          string            `mapstructure:"security_group_id"`
 	SecurityGroupIds         []string          `mapstructure:"security_group_ids"`
 	SubnetId                 string            `mapstructure:"subnet_id"`
 	TemporaryKeyPairName     string            `mapstructure:"temporary_key_pair_name"`

builder/amazon/ebs/builder.go

@@ -150,7 +150,10 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 				b.config.RunConfig.Comm.SSHUsername),
 		},
 		&common.StepProvision{},
-		&stepStopInstance{SpotPrice: b.config.SpotPrice},
+		&stepStopInstance{
+      SpotPrice: b.config.SpotPrice,
+      DisableStopInstance: b.config.DisableStopInstance,
+    },
 		// TODO(mitchellh): verify works with spots
 		&stepModifyInstance{},
 		&awscommon.StepDeregisterAMI{

builder/amazon/ebs/step_stop_instance.go

@@ -11,6 +11,7 @@ import (
 
 type stepStopInstance struct {
 	SpotPrice string
+  DisableStopInstance bool
 }
 
 func (s *stepStopInstance) Run(state multistep.StateBag) multistep.StepAction {
@@ -23,17 +24,21 @@ func (s *stepStopInstance) Run(state multistep.StateBag) multistep.StepAction {
 		return multistep.ActionContinue
 	}
 
-	// Stop the instance so we can create an AMI from it
-	ui.Say("Stopping the source instance...")
-	_, err := ec2conn.StopInstances(&ec2.StopInstancesInput{
-		InstanceIds: []*string{instance.InstanceId},
-	})
-	if err != nil {
-		err := fmt.Errorf("Error stopping instance: %s", err)
-		state.Put("error", err)
-		ui.Error(err.Error())
-		return multistep.ActionHalt
-	}
+  var err error
+
+  if s.DisableStopInstance == false {
+	  // Stop the instance so we can create an AMI from it
+	  ui.Say("Stopping the source instance...")
+	  _, err = ec2conn.StopInstances(&ec2.StopInstancesInput{
+	  	InstanceIds: []*string{instance.InstanceId},
+	  })
+	  if err != nil {
+	  	err := fmt.Errorf("Error stopping instance: %s", err)
+	  	state.Put("error", err)
+	  	ui.Error(err.Error())
+	  	return multistep.ActionHalt
+	  }
+  }
 
 	// Wait for the instance to actual stop
 	ui.Say("Waiting for the instance to stop...")