Add fields to support new volume encryption feature in Nova

 This blueprint is related to the new Nova feature proposed in https://blueprints.launchpad.net/nova/+spec/encrypt-cinder-volumes

Changes have been made in Nova to allow for Cinder volumes to be encrypted when attached to an instance. When a volume is created, a metadata tag is created to indicate the encryption (or lack thereof) for that volume. This blueprint is to expose that functionality to users through Horizon. When creating a volume, a new form field will be added to allow the user to select encryption for the volume. The encryption field can be disabled/hidden via a setting flag. When displaying detailed information for a volume, a new section will be added to display all metadata for a volume.