Join instances column before expecting it to exist
Join instances column before expecting it to exist

test_create_instance_associates_security_groups was fetching a
security group without joining instances, then testing its instances
association. This causes the instances to be fetched after the db api
call has completed, and does not work when explicitly scoping a db
transaction to a db api call.

This change updates the test to explicitly fetch instances. We also
cleanup the test slightly, and add an additional assertion that the
retrieved group is the one we expected.

Change-Id: I11025d9ad13678760eae584951db22090a513645

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