Fixed kompose build failure

While `local` build, kompose was not recognizing `dockerfile` key
Hence it was breaking the build as mentioned in issue #832.
This PR will fix the issue.

pkg/transformer/utils.go

@@ -210,7 +210,16 @@ func BuildDockerImage(service kobject.ServiceConfig, name string, relativePath s
 
 	// Get the appropriate image source and name
 	// use path.Base to get the last element of the relative build path
-	imagePath := path.Join(relativePath, path.Base(service.Build))
+	var imagePath string
+	if service.Dockerfile != "" {
+		//imagePath = path.Join(relativePath, service.Build)
+		dockerfile_dir, _ := path.Split(service.Dockerfile)
+		//imagePath = path.Join(imagePath, dockerfile_dir)
+		imagePath = path.Join(relativePath, service.Build, dockerfile_dir)
+	} else {
+		imagePath = path.Join(relativePath, service.Build)
+	}
+
 	imageName := name
 	if service.Image != "" {
 		imageName = service.Image

script/test/fixtures/buildconfig/docker-compose-dockerfile.yml

@@ -0,0 +1,8 @@
+version: "2"
+
+services:
+    foo:
+        build:
+          context: .
+          dockerfile: build/Dockerfile
+        image: docker.io/cdrage/foobar