Fixes EGI-FCTF/rOCCI-server#36, fixes EGI-FCTF/rOCCI-server#37

Handling `OpenNebula::Error::EACTION` as the 4xx error class.
Merge pull request #41 from arax/err_hndl_fix

Fixes EGI-FCTF/rOCCI-server#36, fixes EGI-FCTF/rOCCI-server#37