refactor: extract _terminate_volume_connections
refactor: extract _terminate_volume_connections

Extract _terminate_volume_connections method, to remove code
duplication.

Change-Id: Ib9bede24d051700fe297fdd5a619f4a3a21bb88e

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