Clean repository after each checkout

Previously, when checking out a tag, folders that had only existed in the previous tag (e.g., `extras/test` when going
from [email protected] to [email protected]) were left behind as empty, and would pollute the library
archives.

So it's necessary to do a clean on the repository after each checkout to remove any untracked objects.

Author: per1234

libraries/git_integration_test.go

@@ -47,6 +47,8 @@ func TestUpdateLibraryJson(t *testing.T) {
 		require.NoError(t, err)
 		err = repoTree.Checkout(&git.CheckoutOptions{Hash: *resolvedTag, Force: true})
 		require.NoError(t, err)
+		err = repoTree.Clean(&git.CleanOptions{Dir: true})
+		require.NoError(t, err)
 
 		library, err := GenerateLibraryFromRepo(r)
 		require.NoError(t, err)

sync_libraries.go

@@ -244,6 +244,10 @@ func syncLibraryTaggedRelease(logger *log.Logger, repo *libraries.Repository, ta
 		return fmt.Errorf("Error checking out repo: %s", err)
 	}
 
+	if err = repoTree.Clean(&git.CleanOptions{Dir: true}); err != nil {
+		return fmt.Errorf("Error cleaning repo: %s", err)
+	}
+
 	// Create library metadata from library.properties
 	library, err := libraries.GenerateLibraryFromRepo(repo)
 	if err != nil {