Change instance disappeared during destroy from Error to Warning
Change instance disappeared during destroy from Error to Warning

Currently Nova logs an error if a libvirt domain disappears during
while waiting for it to be destroyed, but the code actually treats
this (correctly) as a recoverable situation since the end result
is the required one. Hence this should be logged as a warning not
an error.

Change-Id: Ie72cd11e22c5f049d3263e58bec286914798147a
Closes-bug: #1336767

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