Stop volume_type_encryption creation when in use

This bug fix addresses bug #1274252.  It requires a volume
type to have no volumes with the type before allowing it
to be made encrypted.  This prevents a situation where
non-encrypted volumes could have an encrypted volume type.
This fix also adds a unit test to confirm functionality.

Change-Id: Iab0954c2d0af73bce28be7fa319b8b34ca20e720
Closes-Bug: #1274252
Merge "Stop volume_type_encryption creation when in use"