Fix get_roles method of User model

Previous implementation was associating resources with all
the roles regardless of user role in the resource. ie:
if user is cfp member of conf1, the method was returning:
{ organizer => conf1,
  cfp => conf1,
  Info Desk => conf1,
  Volunteers Coordinator => conf1
}

spec/helpers/application_helper_spec.rb

@@ -0,0 +1,10 @@
+require 'spec_helper'
+
+describe ApplicationHelper, type: :helper do
+  describe 'show_roles' do
+    it 'formats the hash passed' do
+      roles = { 'organizer' => ['oSC16', 'oSC15'], 'cfp' => ['oSC16'] }
+      expect(show_roles(roles)).to eq 'Organizer (oSC16, oSC15), Cfp (oSC16)'
+    end
+  end
+end