packer: Put Builder definition into its own file

packer/build.go

@@ -22,20 +22,6 @@ type coreBuild struct {
 	prepareCalled bool
 }
 
-// Implementers of Builder are responsible for actually building images
-// on some platform given some configuration.
-//
-// Prepare is responsible for reading in some configuration, in the raw form
-// of map[string]interface{}, and storing that state for use later. Any setup
-// should be done in this method. Note that NO side effects should really take
-// place in prepare. It is meant as a state setup step only.
-//
-// Run is where the actual build should take place. It takes a Build and a Ui.
-type Builder interface {
-	Prepare(config interface{}) error
-	Run(build Build, ui Ui)
-}
-
 // Returns the name of the build.
 func (b *coreBuild) Name() string {
 	return b.name

packer/builder.go

@@ -0,0 +1,16 @@
+package packer
+
+// Implementers of Builder are responsible for actually building images
+// on some platform given some configuration.
+//
+// Prepare is responsible for reading in some configuration, in the raw form
+// of map[string]interface{}, and storing that state for use later. Any setup
+// should be done in this method. Note that NO side effects should really take
+// place in prepare. It is meant as a state setup step only.
+//
+// Run is where the actual build should take place. It takes a Build and a Ui.
+type Builder interface {
+	Prepare(config interface{}) error
+	Run(build Build, ui Ui)
+}
+