Fix credentials passed to tempest
Fix credentials passed to tempest

Tempest auth Manager recently changed to enforce the use of
Credentials objects in its public interface. Change lets tempest
take the CONF.identity defaults and decide how best to authorize.

Change-Id: If116d8cef145c310bd3a7077b3ae9780e705dc89
Closes-Bug: 1317549

olivierlemasle/murano,telefonicaid/murano,NeCTAR-RC/murano,satish-avninetworks/murano,openstack/murano,DavidPurcell/murano_temp,DavidPurcell/murano_temp,satish-avninetworks/murano,satish-avninetworks/murano,sergmelikyan/murano,chenyujie/hybrid-murano,DavidPurcell/murano_temp,sergmelikyan/murano,sajuptpm/murano,NeCTAR-RC/murano,openstack/murano,DavidPurcell/murano_temp,olivierlemasle/murano,NeCTAR-RC/murano,telefonicaid/murano,olivierlemasle/murano,ativelkov/murano-api,ativelkov/murano-api,NeCTAR-RC/murano,olivierlemasle/murano,chenyujie/hybrid-murano,satish-avninetworks/murano,sajuptpm/murano