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/cgroups/systemd/systemd_test.go

@@ -13,7 +13,7 @@ import (
 )
 
 func TestSystemdVersion(t *testing.T) {
-	var systemdVersionTests = []struct {
+	systemdVersionTests := []struct {
 		verStr      string
 		expectedVer int
 		expectErr   bool