Use gofumpt to format code

gofumpt (mvdan.cc/gofumpt) is a fork of gofmt with stricter rules.

Brought to you by

	git ls-files \*.go | grep -v ^vendor/ | xargs gofumpt -s -w

Looking at the diff, all these changes make sense.

Also, replace gofmt with gofumpt in golangci.yml.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/utils/utils_test.go

@@ -32,7 +32,7 @@ func TestSearchLabels(t *testing.T) {
 
 func TestResolveRootfs(t *testing.T) {
 	dir := "rootfs"
-	if err := os.Mkdir(dir, 0600); err != nil {
+	if err := os.Mkdir(dir, 0o600); err != nil {
 		t.Fatal(err)
 	}
 	defer os.Remove(dir)