Make level_value accept string integers

When a VisibilityLevel is an integer formatted as a string, convert it
to an integer, instead of looking it up in the hash map.

When the value is not recognized, default to PRIVATE.

lib/gitlab/visibility_level.rb

@@ -96,8 +96,8 @@ module Gitlab
       end
 
       def level_value(level)
-        return string_options[level] if level.is_a? String
-        level
+        return level.to_i if level.to_i.to_s == level.to_s && string_options.key(level.to_i)
+        string_options[level] || PRIVATE
       end
 
       def string_level(level)

spec/lib/gitlab/visibility_level_spec.rb

+require 'spec_helper'
+
+describe Gitlab::VisibilityLevel, lib: true do
+  describe '.level_value' do
+    it 'converts "public" to integer value' do
+      expect(described_class.level_value('public')).to eq(Gitlab::VisibilityLevel::PUBLIC)
+    end
+
+    it 'converts string integer to integer value' do
+      expect(described_class.level_value('20')).to eq(20)
+    end
+
+    it 'defaults to PRIVATE when string value is not valid' do
+      expect(described_class.level_value('invalid')).to eq(Gitlab::VisibilityLevel::PRIVATE)
+    end
+
+    it 'defaults to PRIVATE when integer value is not valid' do
+      expect(described_class.level_value(100)).to eq(Gitlab::VisibilityLevel::PRIVATE)
+    end
+  end
+end