Add gometalinter to pre-commit hook

Enable varcheck and fix found issues

Add ineffassign to list of checks and fix found issues

Added nakedret and fixed found issues

Add interfacer check and fix found issue

Add lll and fix found issues

Add deadcode linter, remove unused code

pkg/diff/program.go

@@ -39,11 +39,10 @@ func newProgram(out, errOut io.Writer) *program {
 }
 
 func (d *program) makeCommand(args ...string) exec.Cmd {
-	diff := ""
+	diff := "diff"
 	if envDiff := os.Getenv("KUBERNETES_EXTERNAL_DIFF"); envDiff != "" {
 		diff = envDiff
 	} else {
-		diff = "diff"
 		args = append([]string{"-u", "-N"}, args...)
 	}
 	cmd := exec.New().Command(diff, args...)