Don't setup identity v3 client if v3 is disabled
Don't setup identity v3 client if v3 is disabled

Some tests report failures about the identity v3 url not being
specified, even if api_v3 is set to false in tempest.conf.

Change-Id: Ifb5c6c8bd154373d33c90236ff37fcc5b8759405
Closes-Bug: #1389742

masayukig/tempest,xbezdick/tempest,pandeyop/tempest,jaspreetw/tempest,hpcloud-mon/tempest,JioCloud/tempest,tudorvio/tempest,bigswitch/tempest,tonyli71/tempest,hpcloud-mon/tempest,hayderimran7/tempest,Tesora/tesora-tempest,dkalashnik/tempest,openstack/tempest,bigswitch/tempest,danielmellado/tempest,zsoltdudas/lis-tempest,nunogt/tempest,Juniper/tempest,Lilywei123/tempest,Vaidyanath/tempest,pczerkas/tempest,pandeyop/tempest,LIS/lis-tempest,rakeshmi/tempest,varunarya10/tempest,tudorvio/tempest,vedujoshi/tempest,afaheem88/tempest_neutron,roopali8/tempest,danielmellado/tempest,cisco-openstack/tempest,masayukig/tempest,zsoltdudas/lis-tempest,FujitsuEnablingSoftwareTechnologyGmbH/tempest,FujitsuEnablingSoftwareTechnologyGmbH/tempest,alinbalutoiu/tempest,rzarzynski/tempest,CiscoSystems/tempest,varunarya10/tempest,ebagdasa/tempest,redhat-cip/tempest,Lilywei123/tempest,Vaidyanath/tempest,openstack/tempest,afaheem88/tempest,flyingfish007/tempest,nunogt/tempest,flyingfish007/tempest,hayderimran7/tempest,izadorozhna/tempest,akash1808/tempest,Juraci/tempest,jaspreetw/tempest,redhat-cip/tempest,LIS/lis-tempest,yamt/tempest,sebrandon1/tempest,alinbalutoiu/tempest,tonyli71/tempest,sebrandon1/tempest,akash1808/tempest,xbezdick/tempest,Juraci/tempest,rakeshmi/tempest,JioCloud/tempest,afaheem88/tempest,eggmaster/tempest,NexusIS/tempest,pczerkas/tempest,manasi24/jiocloud-tempest-qatempest,neerja28/Tempest,CiscoSystems/tempest,ebagdasa/tempest,rzarzynski/tempest,jamielennox/tempest,afaheem88/tempest_neutron,manasi24/tempest,neerja28/Tempest,vedujoshi/tempest,manasi24/tempest,roopali8/tempest,NexusIS/tempest,cisco-openstack/tempest,Juniper/tempest,dkalashnik/tempest,izadorozhna/tempest,jamielennox/tempest,yamt/tempest,manasi24/jiocloud-tempest-qatempest,eggmaster/tempest,Tesora/tesora-tempest