Being more defensive around the use_ipv6 config option
Being more defensive around the use_ipv6 config option

fixes bug 1175725

Will allow for the flag to be set to filter out ipv6 if
configured but will not add ipv6 to template if ipv6 is not
configured in quantum. This will allow spwan to continue
working in the case where ipv6 is not configured but flag
use_ipv6 is set in nova.

Change-Id: I26ebdff81efcdeff827521cec247d2c443a5e0ad

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