initialize objects with context in Migration object tests
initialize objects with context in Migration object tests

These changes aim to clean up the pattern of passing a context in
object member functions create/destroy/refresh/save and instead
initialize the object with the context when it's constructed.

Related to blueprint kilo-objects

Change-Id: I0278394942bab138adfbe738668a69368eb38feb

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