Refactor to remove duplicate code
Refactor to remove duplicate code

This change reuses the get_volume_type_encryption function for the
implementation of the is_encrypted function.

Change-Id: Ie6434016840c20229b3a32b676aa8fc994f9362b

Hybrid-Cloud/cinder,duhzecca/cinder,sasukeh/cinder,potsmaster/cinder,winndows/cinder,scality/cinder,sasukeh/cinder,nikesh-mahalka/cinder,manojhirway/ExistingImagesOnNFS,scottdangelo/RemoveVolumeMangerLocks,ge0rgi/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,manojhirway/ExistingImagesOnNFS,winndows/cinder,Datera/cinder,leilihh/cinder,nexusriot/cinder,bswartz/cinder,takeshineshiro/cinder,NetApp/cinder,mahak/cinder,dims/cinder,Nexenta/cinder,Paul-Ezell/cinder-1,duhzecca/cinder,cloudbase/cinder,NetApp/cinder,openstack/cinder,tlakshman26/cinder-new-branch,Hybrid-Cloud/cinder,dims/cinder,apporc/cinder,eharney/cinder,takeshineshiro/cinder,potsmaster/cinder,Paul-Ezell/cinder-1,j-griffith/cinder,Datera/cinder,phenoxim/cinder,cloudbase/cinder,bswartz/cinder,Nexenta/cinder,phenoxim/cinder,j-griffith/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,mahak/cinder,nexusriot/cinder,scottdangelo/RemoveVolumeMangerLocks,openstack/cinder,leilihh/cinder,scality/cinder,eharney/cinder,tlakshman26/cinder-new-branch,apporc/cinder,nikesh-mahalka/cinder