Add encryption indicator for volumes

This patch adds support to horizon for a volume encryption
indicator, to display to the user when a volume has an encrypted
volume type. It uses a change made in cinder
(https://review.openstack.org/#/c/72483/) to determine whether
a volume is encrypted or not.

The patch adds an "Encrypted?" column to the project volumes
table, which has the value "Yes" if the volume is encrypted,
and "No" otherwise.  This column is also included in the
admin volumes table.

Implements: blueprint integration-with-cinder-volume-encryption

Change-Id: I2913b96a704d1183606f9fdd970b14a02956e2bb
Merge "Add encryption indicator for volumes"