Fix prep_resize() stale system_metadata issue
Fix prep_resize() stale system_metadata issue

In compute manager, the _prep_resize() method can clobber the
caller's instance['system_metadata'] if it is in dict format,
and leave's the caller's instance object stale after an update.
This seemingly obscure fix isn't hit until the next patch where
we actually have a way to encounter this specific situation.

Related to blueprint compute-api-objects

Change-Id: I4b3a20c483dd632149c7808daf4986c00dc72890

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