builder/amazon-ebssurrogate: Exclude duplicate root volume

This commit removes the root volume from the list of launch block device
mappings passed to the image, since it is already passed in the form of
a snapshot (which is then configured to be the root device). Without
this commit, AMIs created using this builder have two root volumes
attached on launch.

builder/amazon/ebssurrogate/step_register_ami.go

@@ -24,15 +24,23 @@ func (s *StepRegisterAMI) Run(state multistep.StateBag) multistep.StepAction {
 
 	ui.Say("Registering the AMI...")
 
-	blockDevices := s.BlockDevices
-	blockDevices = append(blockDevices, s.RootDevice.createBlockDeviceMapping(snapshotId))
+	blockDevicesExcludingRoot := make([]*ec2.BlockDeviceMapping, 0, len(s.BlockDevices)-1)
+	for _, blockDevice := range s.BlockDevices {
+		if *blockDevice.DeviceName == s.RootDevice.SourceDeviceName {
+			continue
+		}
+
+		blockDevicesExcludingRoot = append(blockDevicesExcludingRoot, blockDevice)
+	}
+
+	blockDevicesExcludingRoot = append(blockDevicesExcludingRoot, s.RootDevice.createBlockDeviceMapping(snapshotId))
 
 	registerOpts := &ec2.RegisterImageInput{
 		Name:                &config.AMIName,
 		Architecture:        aws.String(ec2.ArchitectureValuesX8664),
 		RootDeviceName:      aws.String(s.RootDevice.DeviceName),
 		VirtualizationType:  aws.String(config.AMIVirtType),
-		BlockDeviceMappings: blockDevices,
+		BlockDeviceMappings: blockDevicesExcludingRoot,
 	}
 
 	if config.AMIEnhancedNetworking {