Use a task subclass instead of a functor + task wrapper
Use a task subclass instead of a functor + task wrapper

Instead of using a functor that activates the scheduler driver
instead incorporate and use a task subclass, this avoids the less
meaningful information that is presented when a functor is used
as well as allows for a more straightforward path for future
subclassing and derivations of work.

Change-Id: Ice66e109968c28f36156edf3dd47a89f94494bb8

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