split up BlockDevices in amazon/common

This breaks up the two options provided by BlockDevices into separate
structs to allow only one of them to be used by the amazon-chroot
builder.

builder/amazon/common/block_device.go

@@ -22,7 +22,15 @@ type BlockDevice struct {
 }
 
 type BlockDevices struct {
-	AMIMappings    []BlockDevice `mapstructure:"ami_block_device_mappings"`
+	AMIBlockDevices    `mapstructure:",squash"`
+	LaunchBlockDevices `mapstructure:",squash"`
+}
+
+type AMIBlockDevices struct {
+	AMIMappings []BlockDevice `mapstructure:"ami_block_device_mappings"`
+}
+
+type LaunchBlockDevices struct {
 	LaunchMappings []BlockDevice `mapstructure:"launch_block_device_mappings"`
 }
 
@@ -77,10 +85,10 @@ func (b *BlockDevices) Prepare(ctx *interpolate.Context) []error {
 	return nil
 }
 
-func (b *BlockDevices) BuildAMIDevices() []*ec2.BlockDeviceMapping {
+func (b *AMIBlockDevices) BuildAMIDevices() []*ec2.BlockDeviceMapping {
 	return buildBlockDevices(b.AMIMappings)
 }
 
-func (b *BlockDevices) BuildLaunchDevices() []*ec2.BlockDeviceMapping {
+func (b *LaunchBlockDevices) BuildLaunchDevices() []*ec2.BlockDeviceMapping {
 	return buildBlockDevices(b.LaunchMappings)
 }

builder/amazon/common/block_device_test.go

@@ -124,22 +124,26 @@ func TestBlockDevice(t *testing.T) {
 	}
 
 	for _, tc := range cases {
-		blockDevices := BlockDevices{
-			AMIMappings:    []BlockDevice{*tc.Config},
+		amiBlockDevices := AMIBlockDevices{
+			AMIMappings: []BlockDevice{*tc.Config},
+		}
+
+		launchBlockDevices := LaunchBlockDevices{
 			LaunchMappings: []BlockDevice{*tc.Config},
 		}
 
 		expected := []*ec2.BlockDeviceMapping{tc.Result}
-		got := blockDevices.BuildAMIDevices()
-		if !reflect.DeepEqual(expected, got) {
+
+		amiResults := amiBlockDevices.BuildAMIDevices()
+		if !reflect.DeepEqual(expected, amiResults) {
 			t.Fatalf("Bad block device, \nexpected: %#v\n\ngot: %#v",
-				expected, got)
+				expected, amiResults)
 		}
 
-		if !reflect.DeepEqual(expected, blockDevices.BuildLaunchDevices()) {
+		launchResults := launchBlockDevices.BuildLaunchDevices()
+		if !reflect.DeepEqual(expected, launchResults) {
 			t.Fatalf("Bad block device, \nexpected: %#v\n\ngot: %#v",
-				expected,
-				blockDevices.BuildLaunchDevices())
+				expected, launchResults)
 		}
 	}
 }