Merge pull request #174 from telefonicaid/bug/173

bug/172
Merge pull request #177 from telefonicaid/hardening/172

hardening/173
Support multi-namenode configuration
Modify the tests according to the multi-namenode support
Delete unnecessary HttpFSBackend and WebHDFSBackend, now we use HDFSBackendImpl
Modigy the README and the template in order to explain the multi-namenode support
Fix issues raised during code review
Merge pull request #180 from telefonicaid/hardening/175

hardening/175 (into develop)