packer: coreBuild.Cancel calls the builder Cancel method

packer/build.go

@@ -91,4 +91,5 @@ func (b *coreBuild) Run(ui Ui) Artifact {
 
 // Cancels the build if it is running.
 func (b *coreBuild) Cancel() {
+	b.builder.Cancel()
 }

packer/build_test.go

@@ -92,3 +92,15 @@ func TestBuild_RunBeforePrepare(t *testing.T) {
 
 	testBuild().Run(testUi())
 }
+
+func TestBuild_Cancel(t *testing.T) {
+	assert := asserts.NewTestingAsserts(t, true)
+
+	build := testBuild()
+	build.Cancel()
+
+	coreB := build.(*coreBuild)
+
+	builder := coreB.builder.(*TestBuilder)
+	assert.True(builder.cancelCalled, "cancel should be called")
+}