Refactor with LDAP spec helpers

spec/lib/gitlab/ldap/user_spec.rb

 require 'spec_helper'
 
 describe Gitlab::LDAP::User do
+  include LdapHelpers
+
   let(:ldap_user) { described_class.new(auth_hash) }
   let(:gl_user) { ldap_user.gl_user }
   let(:info) do
@@ -174,8 +176,7 @@ describe Gitlab::LDAP::User do
 
   describe 'blocking' do
     def configure_block(value)
-      allow_any_instance_of(Gitlab::LDAP::Config)
-        .to receive(:block_auto_created_users).and_return(value)
+      stub_ldap_config(block_auto_created_users: value)
     end
 
     context 'signup' do
@@ -268,7 +269,7 @@ describe Gitlab::LDAP::User do
   describe '#in_any_external_group?' do
     context 'when there is an external group' do
       before do
-        expect_any_instance_of(Gitlab::LDAP::Config).to receive(:external_groups).and_return(['foo'])
+        stub_ldap_config(external_groups: ['foo'])
       end
 
       context 'when the user is in an external group' do
@@ -294,7 +295,7 @@ describe Gitlab::LDAP::User do
 
     context 'when are no external groups' do
       before do
-        expect_any_instance_of(Gitlab::LDAP::Config).to receive(:external_groups).and_return([])
+        stub_ldap_config(external_groups: [])
       end
 
       it 'returns false' do