xenapi: Stub out _add_torrent_url for Vhd tests
xenapi: Stub out _add_torrent_url for Vhd tests

This will make the FetchVhdImageTestCasetest case play nicer when
a BitTorrent url plugin is installed and the tests are running with
no virtual environment.

Change-Id: I204f14246938981633989654bd3446ca3230c222

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