Use User#has_full_private_access? to check if user has Private access

CE and EE implement this differently, so abstract it out of VisibilityLevel.

lib/gitlab/visibility_level.rb

@@ -28,7 +28,7 @@ module Gitlab
       def levels_for_user(user = nil)
         return [PUBLIC] unless user
 
-        if user.admin_or_auditor?
+        if user.has_full_private_access?
           [PRIVATE, INTERNAL, PUBLIC]
         elsif user.external?
           [PUBLIC]

spec/lib/gitlab/ee/visibility_level_spec.rb

+require 'spec_helper'
+
+describe Gitlab::VisibilityLevel, lib: true do
+  describe '.levels_for_user' do
+    it 'returns all levels for an auditor' do
+      user = build(:user, :auditor)
+
+      expect(described_class.levels_for_user(user)).
+        to eq([Gitlab::VisibilityLevel::PRIVATE,
+               Gitlab::VisibilityLevel::INTERNAL,
+               Gitlab::VisibilityLevel::PUBLIC])
+    end
+  end
+end

spec/lib/gitlab/visibility_level_spec.rb

@@ -21,7 +21,7 @@ describe Gitlab::VisibilityLevel, lib: true do
 
   describe '.levels_for_user' do
     it 'returns all levels for an admin' do
-      user = double(:user, admin?: true)
+      user = build(:user, :admin)
 
       expect(described_class.levels_for_user(user)).
         to eq([Gitlab::VisibilityLevel::PRIVATE,
@@ -30,7 +30,7 @@ describe Gitlab::VisibilityLevel, lib: true do
     end
 
     it 'returns INTERNAL and PUBLIC for internal users' do
-      user = double(:user, admin?: false, external?: false)
+      user = build(:user)
 
       expect(described_class.levels_for_user(user)).
         to eq([Gitlab::VisibilityLevel::INTERNAL,
@@ -38,7 +38,7 @@ describe Gitlab::VisibilityLevel, lib: true do
     end
 
     it 'returns PUBLIC for external users' do
-      user = double(:user, admin?: false, external?: true)
+      user = build(:user, :external)
 
       expect(described_class.levels_for_user(user)).
         to eq([Gitlab::VisibilityLevel::PUBLIC])