Optimalization of getRequiredAttributes() for list of services

 - Fix of FIXME in getRequiredAttributes(List<Service>, Resource)  
   - Added method getRequiredAttributes(sess, resource, List<Service>) in AttributesManagerBl
   - Added method getRequiredAttributes(sess, resource, List<Service> serviceIds) in AttributesManagerImpl
 - Added test for getRequiredAttributes(sess, List<Service>, resource)