Added verbose error message in tests helper mixin
Added verbose error message in tests helper mixin

blueprint db-api-tests

Change-Id: I2fcfc50824de8965fe8521cde5f20d24e88eb8ae

bgxavier/nova,OpenAcademy-OpenStack/nova-scheduler,saleemjaveds/https-github.com-openstack-nova,zaina/nova,hanlind/nova,BeyondTheClouds/nova,eayunstack/nova,cloudbase/nova-virtualbox,shail2810/nova,CCI-MOC/nova,zhimin711/nova,NeCTAR-RC/nova,varunarya10/nova_test_latest,akash1808/nova,gooddata/openstack-nova,projectcalico/calico-nova,iuliat/nova,Yusuke1987/openstack_template,whitepages/nova,bigswitch/nova,Juniper/nova,adelina-t/nova,JioCloud/nova,Juniper/nova,yosshy/nova,hanlind/nova,OpenAcademy-OpenStack/nova-scheduler,takeshineshiro/nova,klmitch/nova,maelnor/nova,viggates/nova,rajalokan/nova,tianweizhang/nova,JioCloud/nova_test_latest,SUSE-Cloud/nova,fnordahl/nova,LoHChina/nova,petrutlucian94/nova,belmiromoreira/nova,barnsnake351/nova,virtualopensystems/nova,BeyondTheClouds/nova,LoHChina/nova,raildo/nova,zzicewind/nova,rickerc/nova_audit,fnordahl/nova,sebrandon1/nova,Metaswitch/calico-nova,jianghuaw/nova,SUSE-Cloud/nova,vmturbo/nova,rahulunair/nova,mgagne/nova,eayunstack/nova,dims/nova,klmitch/nova,JioCloud/nova,cloudbase/nova,iuliat/nova,devendermishrajio/nova_test_latest,Brocade-OpenSource/OpenStack-DNRM-Nova,redhat-openstack/nova,saleemjaveds/https-github.com-openstack-nova,bgxavier/nova,CEG-FYP-OpenStack/scheduler,isyippee/nova,mikalstill/nova,vmturbo/nova,TwinkleChawla/nova,barnsnake351/nova,vladikr/nova_drafts,badock/nova,Yuriy-Leonov/nova,redhat-openstack/nova,CloudServer/nova,ted-gould/nova,DirectXMan12/nova-hacking,cloudbase/nova-virtualbox,JioCloud/nova_test_latest,bclau/nova,citrix-openstack-build/nova,qwefi/nova,devoid/nova,sacharya/nova,Juniper/nova,MountainWei/nova,rrader/nova-docker-plugin,Metaswitch/calico-nova,affo/nova,maelnor/nova,whitepages/nova,edulramirez/nova,petrutlucian94/nova,ewindisch/nova,tangfeixiong/nova,double12gzh/nova,tianweizhang/nova,alvarolopez/nova,belmiromoreira/nova,BeyondTheClouds/nova,isyippee/nova,cloudbase/nova,kimjaejoong/nova,rahulunair/nova,blueboxgroup/nova,DirectXMan12/nova-hacking,tanglei528/nova,felixma/nova,vmturbo/nova,cloudbau/nova,cloudbase/nova,petrutlucian94/nova_dev,takeshineshiro/nova,Yusuke1987/openstack_template,tudorvio/nova,berrange/nova,angdraug/nova,ted-gould/nova,zaina/nova,kimjaejoong/nova,shahar-stratoscale/nova,devoid/nova,adelina-t/nova,dawnpower/nova,eonpatapon/nova,TieWei/nova,MountainWei/nova,thomasem/nova,phenoxim/nova,sebrandon1/nova,mandeepdhami/nova,citrix-openstack-build/nova,dims/nova,qwefi/nova,vmturbo/nova,yatinkumbhare/openstack-nova,jeffrey4l/nova,ntt-sic/nova,shahar-stratoscale/nova,akash1808/nova,j-carpentier/nova,ruslanloman/nova,cernops/nova,openstack/nova,projectcalico/calico-nova,rahulunair/nova,j-carpentier/nova,joker946/nova,angdraug/nova,shootstar/novatest,Tehsmash/nova,watonyweng/nova,tanglei528/nova,leilihh/novaha,alvarolopez/nova,CiscoSystems/nova,devendermishrajio/nova,joker946/nova,devendermishrajio/nova,mmnelemane/nova,plumgrid/plumgrid-nova,raildo/nova,NeCTAR-RC/nova,mikalstill/nova,petrutlucian94/nova_dev,mahak/nova,devendermishrajio/nova_test_latest,edulramirez/nova,leilihh/novaha,mmnelemane/nova,affo/nova,tealover/nova,silenceli/nova,akash1808/nova_test_latest,noironetworks/nova,mandeepdhami/nova,hanlind/nova,ewindisch/nova,mahak/nova,DirectXMan12/nova-hacking,luogangyi/bcec-nova,jianghuaw/nova,imsplitbit/nova,alaski/nova,Stavitsky/nova,silenceli/nova,phenoxim/nova,thomasem/nova,rickerc/nova_audit,shail2810/nova,CloudServer/nova,eharney/nova,viggates/nova,ntt-sic/nova,bclau/nova,sacharya/nova,nikesh-mahalka/nova,noironetworks/nova,rrader/nova-docker-plugin,apporc/nova,badock/nova,zzicewind/nova,klmitch/nova,gooddata/openstack-nova,jeffrey4l/nova,vladikr/nova_drafts,Yuriy-Leonov/nova,blueboxgroup/nova,TwinkleChawla/nova,eonpatapon/nova,openstack/nova,mahak/nova,orbitfp7/nova,Tehsmash/nova,mikalstill/nova,orbitfp7/nova,yatinkumbhare/openstack-nova,tangfeixiong/nova,sebrandon1/nova,CEG-FYP-OpenStack/scheduler,cloudbau/nova,alexandrucoman/vbox-nova-driver,ruslanloman/nova,mgagne/nova,JianyuWang/nova,luogangyi/bcec-nova,CCI-MOC/nova,rajalokan/nova,zhimin711/nova,JianyuWang/nova,jianghuaw/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,yosshy/nova,felixma/nova,cyx1231st/nova,varunarya10/nova_test_latest,rajalokan/nova,scripnichenko/nova,Stavitsky/nova,alaski/nova,cyx1231st/nova,eharney/nova,imsplitbit/nova,nikesh-mahalka/nova,berrange/nova,apporc/nova,akash1808/nova_test_latest,tealover/nova,CiscoSystems/nova,alexandrucoman/vbox-nova-driver,Juniper/nova,spring-week-topos/nova-week,leilihh/nova,shootstar/novatest,virtualopensystems/nova,gooddata/openstack-nova,gooddata/openstack-nova,leilihh/nova,dawnpower/nova,tudorvio/nova,scripnichenko/nova,double12gzh/nova,cernops/nova,rajalokan/nova,spring-week-topos/nova-week,openstack/nova,klmitch/nova,Francis-Liu/animated-broccoli,plumgrid/plumgrid-nova,Francis-Liu/animated-broccoli,watonyweng/nova,TieWei/nova,jianghuaw/nova,cernops/nova,bigswitch/nova