Avoid potential race condition in list_stacks assert.
Avoid potential race condition in list_stacks assert.

Asserting that stack listing has increased by exactly 1
after a create is racy if there are other concurrent stack
operations occuring.

This replaces the assert with a check that confirms the created
stack appears in the stack list.

This race has not actually been triggered yet, but may when tempest
gains some concurrency.

Change-Id: I200efa6d3d55e403c9d9a5f3abc49ad6c024e6a9

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