Elevate volume/snap "is busy" log message for volume/snap_delete
Elevate volume/snap "is busy" log message for volume/snap_delete

If deletion fails because the volume is busy, log at "error" level
rather than "debug" to ensure that the error is logged and visible
to a user.

Change-Id: I04031ee6b1f6647a126baa8a29c15a00b84b27b1

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