avoid error and trace on dom.vcpus() in lxc
avoid error and trace on dom.vcpus() in lxc

This fixes bug 903943.  If you used lxc, you'd eventually
see stack traces in nova-compute due to use of dom.vcpus().

Change-Id: I8ff4e973d33eef3df116feb237b2febc8e6a59b5

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