xenapi: fix undefined variable in logging message
xenapi: fix undefined variable in logging message

When resizing down, a log message references an undefined variable
cow_uuid. This used to exist before some refactoring. Make sure we
get the UUID early enough for the log message, but also change the
name since in the resize down case, we don't use a snapshot and a
COW VDI.

Change-Id: I8cf7fc66aa18fe23ced9144d1b58f89de5d0de80

leilihh/nova,CloudServer/nova,TwinkleChawla/nova,vladikr/nova_drafts,mandeepdhami/nova,noironetworks/nova,tianweizhang/nova,sridevikoushik31/openstack,eayunstack/nova,gspilio/nova,gspilio/nova,shail2810/nova,JioCloud/nova_test_latest,iuliat/nova,citrix-openstack-build/nova,luogangyi/bcec-nova,double12gzh/nova,adelina-t/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,orbitfp7/nova,vladikr/nova_drafts,alvarolopez/nova,Stavitsky/nova,Triv90/Nova,iuliat/nova,felixma/nova,TwinkleChawla/nova,CEG-FYP-OpenStack/scheduler,sebrandon1/nova,luogangyi/bcec-nova,openstack/nova,sridevikoushik31/nova,Francis-Liu/animated-broccoli,MountainWei/nova,jianghuaw/nova,yrobla/nova,Yusuke1987/openstack_template,qwefi/nova,ewindisch/nova,belmiromoreira/nova,yrobla/nova,aristanetworks/arista-ovs-nova,devoid/nova,plumgrid/plumgrid-nova,zzicewind/nova,alexandrucoman/vbox-nova-driver,shootstar/novatest,TieWei/nova,viggates/nova,spring-week-topos/nova-week,mmnelemane/nova,bgxavier/nova,akash1808/nova_test_latest,dims/nova,ruslanloman/nova,Triv90/Nova,blueboxgroup/nova,ntt-sic/nova,fajoy/nova,CCI-MOC/nova,rajalokan/nova,eonpatapon/nova,berrange/nova,felixma/nova,sebrandon1/nova,kimjaejoong/nova,cloudbase/nova-virtualbox,CiscoSystems/nova,CloudServer/nova,maelnor/nova,thomasem/nova,double12gzh/nova,scripnichenko/nova,JioCloud/nova_test_latest,CiscoSystems/nova,Stavitsky/nova,badock/nova,j-carpentier/nova,gspilio/nova,scripnichenko/nova,usc-isi/nova,shahar-stratoscale/nova,raildo/nova,sridevikoushik31/openstack,MountainWei/nova,adelina-t/nova,maoy/zknova,akash1808/nova_test_latest,ted-gould/nova,maheshp/novatest,mmnelemane/nova,rrader/nova-docker-plugin,shootstar/novatest,DirectXMan12/nova-hacking,akash1808/nova,cloudbau/nova,petrutlucian94/nova,Juniper/nova,mandeepdhami/nova,dims/nova,nikesh-mahalka/nova,raildo/nova,rahulunair/nova,bgxavier/nova,jianghuaw/nova,cloudbase/nova,takeshineshiro/nova,bclau/nova,klmitch/nova,petrutlucian94/nova_dev,varunarya10/nova_test_latest,rickerc/nova_audit,devendermishrajio/nova,cloudbase/nova-virtualbox,takeshineshiro/nova,yosshy/nova,JioCloud/nova,maheshp/novatest,tudorvio/nova,angdraug/nova,imsplitbit/nova,BeyondTheClouds/nova,jeffrey4l/nova,Metaswitch/calico-nova,jianghuaw/nova,virtualopensystems/nova,bigswitch/nova,silenceli/nova,vmturbo/nova,sridevikoushik31/nova,affo/nova,jeffrey4l/nova,cyx1231st/nova,mgagne/nova,Francis-Liu/animated-broccoli,redhat-openstack/nova,Metaswitch/calico-nova,zaina/nova,mgagne/nova,OpenAcademy-OpenStack/nova-scheduler,watonyweng/nova,isyippee/nova,varunarya10/nova_test_latest,BeyondTheClouds/nova,tianweizhang/nova,citrix-openstack-build/nova,zhimin711/nova,rrader/nova-docker-plugin,cyx1231st/nova,tanglei528/nova,virtualopensystems/nova,houshengbo/nova_vmware_compute_driver,DirectXMan12/nova-hacking,Tehsmash/nova,rajalokan/nova,leilihh/novaha,Triv90/Nova,JianyuWang/nova,JioCloud/nova,tanglei528/nova,rickerc/nova_audit,Yuriy-Leonov/nova,openstack/nova,hanlind/nova,houshengbo/nova_vmware_compute_driver,jianghuaw/nova,usc-isi/nova,alvarolopez/nova,Juniper/nova,gooddata/openstack-nova,CCI-MOC/nova,silenceli/nova,JianyuWang/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,fnordahl/nova,ntt-sic/nova,spring-week-topos/nova-week,klmitch/nova,viggates/nova,mikalstill/nova,petrutlucian94/nova,bclau/nova,hanlind/nova,mahak/nova,devoid/nova,leilihh/novaha,orbitfp7/nova,rahulunair/nova,sridevikoushik31/nova,dawnpower/nova,TieWei/nova,eharney/nova,qwefi/nova,barnsnake351/nova,ewindisch/nova,shail2810/nova,openstack/nova,bigswitch/nova,usc-isi/nova,Tehsmash/nova,yrobla/nova,Yuriy-Leonov/nova,houshengbo/nova_vmware_compute_driver,eonpatapon/nova,berrange/nova,saleemjaveds/https-github.com-openstack-nova,alexandrucoman/vbox-nova-driver,klmitch/nova,maoy/zknova,NeCTAR-RC/nova,SUSE-Cloud/nova,vmturbo/nova,ted-gould/nova,watonyweng/nova,DirectXMan12/nova-hacking,sacharya/nova,mahak/nova,zhimin711/nova,yatinkumbhare/openstack-nova,devendermishrajio/nova,cloudbase/nova,gooddata/openstack-nova,klmitch/nova,joker946/nova,leilihh/nova,devendermishrajio/nova_test_latest,apporc/nova,Yusuke1987/openstack_template,maoy/zknova,cloudbau/nova,tudorvio/nova,whitepages/nova,joker946/nova,mikalstill/nova,cernops/nova,belmiromoreira/nova,projectcalico/calico-nova,blueboxgroup/nova,phenoxim/nova,gooddata/openstack-nova,j-carpentier/nova,cernops/nova,edulramirez/nova,edulramirez/nova,vmturbo/nova,hanlind/nova,thomasem/nova,sebrandon1/nova,ruslanloman/nova,tealover/nova,whitepages/nova,badock/nova,dawnpower/nova,eharney/nova,redhat-openstack/nova,aristanetworks/arista-ovs-nova,dstroppa/openstack-smartos-nova-grizzly,devendermishrajio/nova_test_latest,alaski/nova,vmturbo/nova,nikesh-mahalka/nova,dstroppa/openstack-smartos-nova-grizzly,NeCTAR-RC/nova,petrutlucian94/nova_dev,fnordahl/nova,yosshy/nova,isyippee/nova,projectcalico/calico-nova,fajoy/nova,akash1808/nova,rajalokan/nova,eayunstack/nova,zaina/nova,zzicewind/nova,angdraug/nova,plumgrid/plumgrid-nova,gooddata/openstack-nova,imsplitbit/nova,fajoy/nova,tangfeixiong/nov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