Fix improper use of Stevedore
Fix improper use of Stevedore

The tests in nova/tests/test_hook.py are mocking a private part
of the stevedore API (_load_plugins). We should use
HookManager.make_test_instance() to create a test version
of an HookManager and use that.

Change-Id: Iafacd9f08e8c714eed071c5ff41c9eeed4e1130c

double12gzh/nova,mahak/nova,zhimin711/nova,orbitfp7/nova,Tehsmash/nova,jianghuaw/nova,gooddata/openstack-nova,alaski/nova,zhimin711/nova,scripnichenko/nova,devendermishrajio/nova_test_latest,mikalstill/nova,rahulunair/nova,jianghuaw/nova,akash1808/nova_test_latest,apporc/nova,cloudbase/nova,alvarolopez/nova,mikalstill/nova,JioCloud/nova_test_latest,tudorvio/nova,yatinkumbhare/openstack-nova,kimjaejoong/nova,varunarya10/nova_test_latest,hanlind/nova,j-carpentier/nova,orbitfp7/nova,gooddata/openstack-nova,zaina/nova,isyippee/nova,affo/nova,jianghuaw/nova,shail2810/nova,TwinkleChawla/nova,adelina-t/nova,eonpatapon/nova,hanlind/nova,mahak/nova,phenoxim/nova,Juniper/nova,mandeepdhami/nova,bigswitch/nova,Francis-Liu/animated-broccoli,openstack/nova,cloudbase/nova,cloudbase/nova-virtualbox,BeyondTheClouds/nova,devendermishrajio/nova,yosshy/nova,zzicewind/nova,phenoxim/nova,JianyuWang/nova,CCI-MOC/nova,tealover/nova,devendermishrajio/nova_test_latest,petrutlucian94/nova,apporc/nova,rajalokan/nova,LoHChina/nova,nikesh-mahalka/nova,gooddata/openstack-nova,akash1808/nova,CloudServer/nova,vmturbo/nova,JianyuWang/nova,Francis-Liu/animated-broccoli,takeshineshiro/nova,Stavitsky/nova,rajalokan/nova,alexandrucoman/vbox-nova-driver,devendermishrajio/nova,cloudbase/nova,felixma/nova,openstack/nova,ted-gould/nova,Juniper/nova,edulramirez/nova,rahulunair/nova,NeCTAR-RC/nova,alexandrucoman/vbox-nova-driver,cyx1231st/nova,klmitch/nova,akash1808/nova_test_latest,jeffrey4l/nova,noironetworks/nova,TwinkleChawla/nova,iuliat/nova,tangfeixiong/nova,watonyweng/nova,ruslanloman/nova,isyippee/nova,klmitch/nova,yosshy/nova,iuliat/nova,MountainWei/nova,MountainWei/nova,scripnichenko/nova,tudorvio/nova,nikesh-mahalka/nova,Yusuke1987/openstack_template,LoHChina/nova,JioCloud/nova,joker946/nova,cernops/nova,cloudbase/nova-virtualbox,affo/nova,rahulunair/nova,alvarolopez/nova,kimjaejoong/nova,BeyondTheClouds/nova,belmiromoreira/nova,takeshineshiro/nova,fnordahl/nova,fnordahl/nova,vmturbo/nova,felixma/nova,mmnelemane/nova,blueboxgroup/nova,petrutlucian94/nova,dims/nova,mikalstill/nova,dawnpower/nova,mandeepdhami/nova,adelina-t/nova,dims/nova,ted-gould/nova,bgxavier/nova,BeyondTheClouds/nova,double12gzh/nova,gooddata/openstack-nova,sebrandon1/nova,CloudServer/nova,tealover/nova,barnsnake351/nova,shail2810/nova,j-carpentier/nova,belmiromoreira/nova,raildo/nova,mahak/nova,Juniper/nova,jianghuaw/nova,jeffrey4l/nova,NeCTAR-RC/nova,dawnpower/nova,rajalokan/nova,Tehsmash/nova,thomasem/nova,openstack/nova,alaski/nova,whitepages/nova,cyx1231st/nova,klmitch/nova,vmturbo/nova,cernops/nova,ruslanloman/nova,edulramirez/nova,raildo/nova,sebrandon1/nova,yatinkumbhare/openstack-nova,CCI-MOC/nova,klmitch/nova,watonyweng/nova,rajalokan/nova,Stavitsky/nova,bgxavier/nova,JioCloud/nova,CEG-FYP-OpenStack/scheduler,akash1808/nova,Juniper/nova,vmturbo/nova,CEG-FYP-OpenStack/scheduler,varunarya10/nova_test_latest,zaina/nova,zzicewind/nova,noironetworks/nova,thomasem/nova,eonpatapon/nova,joker946/nova,barnsnake351/nova,Yusuke1987/openstack_template,bigswitch/nova,hanlind/nova,cernops/nova,blueboxgroup/nova,JioCloud/nova_test_latest,sebrandon1/nova,whitepages/nova,mmnelemane/nova,tangfeixiong/nova