libvirt: convert CacheConcurrencyTestCase to avoid DB usage
libvirt: convert CacheConcurrencyTestCase to avoid DB usage

The CacheConcurrencyTestCase test case does not do anything DB
related. Convert it to NoDBTestCase to avoid DB setup penalty.
This improves perf from 1.7s to 0.2s

Partial-bug: #1369516
Change-Id: I8ef124e9f5d86a990722019978c725c955ffb1ea

affo/nova,yosshy/nova,Tehsmash/nova,maelnor/nova,Yusuke1987/openstack_template,isyippee/nova,nikesh-mahalka/nova,angdraug/nova,gooddata/openstack-nova,cernops/nova,badock/nova,rajalokan/nova,apporc/nova,mikalstill/nova,maelnor/nova,bgxavier/nova,apporc/nova,rahulunair/nova,zaina/nova,yatinkumbhare/openstack-nova,alaski/nova,varunarya10/nova_test_latest,jeffrey4l/nova,kimjaejoong/nova,eonpatapon/nova,raildo/nova,tealover/nova,noironetworks/nova,eayunstack/nova,angdraug/nova,NeCTAR-RC/nova,NeCTAR-RC/nova,ruslanloman/nova,CEG-FYP-OpenStack/scheduler,zaina/nova,mmnelemane/nova,zzicewind/nova,tealover/nova,devendermishrajio/nova_test_latest,scripnichenko/nova,isyippee/nova,takeshineshiro/nova,CloudServer/nova,double12gzh/nova,j-carpentier/nova,Stavitsky/nova,cernops/nova,JioCloud/nova,hanlind/nova,felixma/nova,openstack/nova,noironetworks/nova,scripnichenko/nova,JioCloud/nova,phenoxim/nova,tudorvio/nova,redhat-openstack/nova,mahak/nova,ted-gould/nova,iuliat/nova,Juniper/nova,klmitch/nova,gooddata/openstack-nova,Juniper/nova,edulramirez/nova,vmturbo/nova,Stavitsky/nova,zhimin711/nova,gooddata/openstack-nova,berrange/nova,adelina-t/nova,alvarolopez/nova,dawnpower/nova,barnsnake351/nova,rahulunair/nova,sebrandon1/nova,JioCloud/nova_test_latest,projectcalico/calico-nova,TwinkleChawla/nova,mandeepdhami/nova,Yusuke1987/openstack_template,rajalokan/nova,blueboxgroup/nova,whitepages/nova,vmturbo/nova,blueboxgroup/nova,whitepages/nova,silenceli/nova,vmturbo/nova,Tehsmash/nova,alvarolopez/nova,j-carpentier/nova,orbitfp7/nova,alaski/nova,jianghuaw/nova,badock/nova,thomasem/nova,devendermishrajio/nova,mmnelemane/nova,JianyuWang/nova,cloudbase/nova,zhimin711/nova,affo/nova,akash1808/nova,cloudbase/nova-virtualbox,ruslanloman/nova,mgagne/nova,rajalokan/nova,cyx1231st/nova,varunarya10/nova_test_latest,akash1808/nova,Juniper/nova,tianweizhang/nova,joker946/nova,TwinkleChawla/nova,yosshy/nova,BeyondTheClouds/nova,projectcalico/calico-nova,rahulunair/nova,devendermishrajio/nova_test_latest,nikesh-mahalka/nova,kimjaejoong/nova,bgxavier/nova,CloudServer/nova,redhat-openstack/nova,openstack/nova,belmiromoreira/nova,raildo/nova,devendermishrajio/nova,hanlind/nova,cloudbase/nova,akash1808/nova_test_latest,gooddata/openstack-nova,Francis-Liu/animated-broccoli,mikalstill/nova,akash1808/nova_test_latest,joker946/nova,jianghuaw/nova,jianghuaw/nova,Metaswitch/calico-nova,klmitch/nova,cernops/nova,shail2810/nova,dims/nova,petrutlucian94/nova,tangfeixiong/nova,CCI-MOC/nova,cloudbase/nova,mandeepdhami/nova,cloudbase/nova-virtualbox,zzicewind/nova,cyx1231st/nova,belmiromoreira/nova,jeffrey4l/nova,hanlind/nova,jianghuaw/nova,mahak/nova,vmturbo/nova,MountainWei/nova,alexandrucoman/vbox-nova-driver,sebrandon1/nova,Juniper/nova,mgagne/nova,eonpatapon/nova,openstack/nova,bigswitch/nova,watonyweng/nova,shail2810/nova,silenceli/nova,takeshineshiro/nova,eayunstack/nova,JianyuWang/nova,mahak/nova,bigswitch/nova,Metaswitch/calico-nova,CCI-MOC/nova,barnsnake351/nova,Francis-Liu/animated-broccoli,edulramirez/nova,sebrandon1/nova,mikalstill/nova,yatinkumbhare/openstack-nova,klmitch/nova,dawnpower/nova,LoHChina/nova,CEG-FYP-OpenStack/scheduler,watonyweng/nova,berrange/nova,ted-gould/nova,phenoxim/nova,orbitfp7/nova,tangfeixiong/nova,felixma/nova,LoHChina/nova,BeyondTheClouds/nova,petrutlucian94/nova,klmitch/nova,BeyondTheClouds/nova,JioCloud/nova_test_latest,iuliat/nova,fnordahl/nova,adelina-t/nova,rajalokan/nova,fnordahl/nova,double12gzh/nova,dims/nova,alexandrucoman/vbox-nova-driver,MountainWei/nova,tudorvio/nova,tianweizhang/nova,thomasem/nova