Fix a minor memory leak
Fix a minor memory leak

Fixes a minor memory leak caused by a self-referential data structure
with a __del__() method by explicitly breaking the cycle.

Change-Id: Ic2c896d3067f8a2205abc8a43ec290fdbd92ef09

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