delta: trim path when computing src files set

The path contains an ending "/" which wouldn't match when we walk dst as
it's not there.

That had the unpleasant effect of creating empty folders in the
destinations

pkg/api/core/image/delta_test.go

@@ -79,7 +79,7 @@ var _ = Describe("Delta", func() {
 				)
 				Expect(err).ToNot(HaveOccurred())
 				defer os.RemoveAll(tmpdir) // clean up
-
+				Expect(file.Exists(filepath.Join(tmpdir, "home"))).To(BeFalse())
 				Expect(file.Exists(filepath.Join(tmpdir, "root", ".cache"))).To(BeTrue())
 				Expect(file.Exists(filepath.Join(tmpdir, "bin", "sh"))).To(BeFalse())
 				Expect(file.Exists(filepath.Join(tmpdir, "usr", "local", "go"))).To(BeTrue())

pkg/api/core/image/extract.go

@@ -67,10 +67,17 @@ func ExtractDeltaAdditionsFiles(
 		if err != nil {
 			return nil, err
 		}
-		filesSrc.Set(hdr.Name, "")
+
+		switch hdr.Typeflag {
+		case tar.TypeDir:
+			filesSrc.Set(filepath.Dir(hdr.Name), "")
+		default:
+			filesSrc.Set(hdr.Name, "")
+		}
 	}
 
 	return func(h *tar.Header) (bool, error) {
+
 		fileName := filepath.Join(string(os.PathSeparator), h.Name)
 		_, exists := filesSrc.Get(h.Name)
 		if exists {