Idf84ccff254d26fa13473fe9741ddac21cbcf321 added this check in order for
Nova to avoid booting encrypted images created by Cinder as there is
currently no support for using such images (rotating keys etc).
The check however missed the slightly convoluted use case where this
image property is found against a volume after the volume in question is
created using an encrypted image created by cinder from an encrypted
volume. In other words:
- Cinder creates an encrypted volume A
- Glance creates an encrypted image A from volume A
- Cinder creates an encrypted volume B from image A
- Nova attempts to boot an instance using volume B
Note that Nova may request the creation of volume B or a user could also
do this directly through Cinder.
As such this change simply ensures that the instance isn't booting from
a volume when preforming the check as it is only valid when booting from
an image.
Closes-Bug: #1895696
Change-Id: Ic92cab7362fa25050e5bbef5c3e360108365b5c7
f9b67893ac