Don't set signing_dir by default.
Don't set signing_dir by default.

Allow the auth_token middleware to setup its own signing_dir
if required.

Fixes LP Bug #1185098.

Change-Id: Id8766efb34d37ca382b865167ec2465d0a1ce8dc

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