Use cached db object in volume_mig_status ext
Use cached db object in volume_mig_status ext

There is no need to rerequest the volume object from the db in
the extension because we already have a cached copy in the request.
This can potentially save hundreds of db queries in list.

Change-Id: I46da8c7b6c2af2435d246ebd8e95d4712065f1e7
Resolves-bug: 1308255

mahak/cinder,mahak/cinder,Thingee/cinder,julianwang/cinder,redhat-openstack/cinder,Nexenta/cinder,Paul-Ezell/cinder-1,Hybrid-Cloud/cinder,openstack/cinder,saeki-masaki/cinder,Akrog/cinder,tlakshman26/cinder-new-branch,bswartz/cinder,NetApp/cinder,rakeshmi/cinder,phenoxim/cinder,takeshineshiro/cinder,scottdangelo/RemoveVolumeMangerLocks,alex8866/cinder,winndows/cinder,cloudbase/cinder,scality/cinder,winndows/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,NetApp/cinder,blueboxgroup/cinder,j-griffith/cinder,phenoxim/cinder,j-griffith/cinder,alex8866/cinder,CloudServer/cinder,github-borat/cinder,duhzecca/cinder,leilihh/cinder,JioCloud/cinder,eharney/cinder,hguemar/cinder,Accelerite/cinder,apporc/cinder,manojhirway/ExistingImagesOnNFS,potsmaster/cinder,nexusriot/cinder,nikesh-mahalka/cinder,petrutlucian94/cinder,Thingee/cinder,github-borat/cinder,Datera/cinder,Hybrid-Cloud/cinder,bswartz/cinder,tlakshman26/cinder-new-branch,scality/cinder,cloudbase/cinder,eharney/cinder,duhzecca/cinder,manojhirway/ExistingImagesOnNFS,abusse/cinder,Thingee/cinder,redhat-openstack/cinder,hguemar/cinder,Accelerite/cinder,blueboxgroup/cinder,openstack/cinder,nexusriot/cinder,julianwang/cinder,potsmaster/cinder,dims/cinder,nikesh-mahalka/cinder,CloudServer/cinder,ge0rgi/cinder,Datera/cinder,JioCloud/cinder,Paul-Ezell/cinder-1,Akrog/cinder,apporc/cinder,takeshineshiro/cinder,Nexenta/cinder,scottdangelo/RemoveVolumeMangerLocks,petrutlucian94/cinder,tlakshman26/cinder-https-changes,abusse/cinder,rakeshmi/cinder,saeki-masaki/cinder,sasukeh/cinder,dims/cinder,tlakshman26/cinder-https-changes,leilihh/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,sasukeh/cinder