Makes exception_traceback optional for exception_result
Makes exception_traceback optional for exception_result

Change-Id: Icd6d655e615fbe92bbf7ba6caaffe5b74c67ffab
Closes-Bug: #1428058

satish-avninetworks/murano,DavidPurcell/murano_temp,sajuptpm/murano,olivierlemasle/murano,olivierlemasle/murano,NeCTAR-RC/murano,NeCTAR-RC/murano,olivierlemasle/murano,satish-avninetworks/murano,sajuptpm/murano,DavidPurcell/murano_temp,DavidPurcell/murano_temp,chenyujie/hybrid-murano,NeCTAR-RC/murano,chenyujie/hybrid-murano,olivierlemasle/murano,satish-avninetworks/murano,openstack/murano,NeCTAR-RC/murano,DavidPurcell/murano_temp,satish-avninetworks/murano,openstack/murano