Fix rubocop offenses. It's not checked before when

it's inside lib/tasks/*

.rubocop.yml

@@ -19,6 +19,10 @@ AllCops:
     - 'builds/**/*'
   CacheRootDirectory: tmp
+# TODO: Remove me after updating gitlab-style
+Style/TrailingUnderscoreVariable:
+  Enabled: false
+
 # Gitlab ###################################################################
 Gitlab/ModuleWithInstanceVariables:

lib/gitlab/task_helpers.rb

 require 'rainbow/ext/string'
 require 'gitlab/utils/strong_memoize'
+# rubocop:disable Rails/Output
 module Gitlab
   TaskFailedError = Class.new(StandardError)
   TaskAbortedByUserError = Class.new(StandardError)
@@ -96,11 +97,9 @@ module Gitlab
     end
     def gid_for(group_name)
-      begin
-        Etc.getgrnam(group_name).gid
-      rescue ArgumentError # no group
-        "group #{group_name} doesn't exist"
-      end
+      Etc.getgrnam(group_name).gid
+    rescue ArgumentError # no group
+      "group #{group_name} doesn't exist"
     end
     def gitlab_user