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

 - Added test for getRequiresAttributes(sess, List<Service>, resource)
Merge branch 'requiredAttrs' of https://github.com/papperwing/perun into kubaTask03-requiredAttrs
Fix typo and make test more complex
Merge pull request #339 from stavamichal/kubaTask03-requiredAttrs

Kuba task03 required attrs